Scott Jacqmein, a 52-year-old actor in Dallas, fields one or two texts a week from acquaintances and friends who are pretty sure they have seen him pitching a peculiar range of businesses on TikTok. There was an insurance-quote marketplace, a daily horoscope app, and a puzzle and brain teaser app, the last of which featured him speaking fluent Spanish.

But the ads seem a little off to them. Mr. Jacqmein doesn’t speak Spanish, he’s missing his trademark facial hair, and the voice and gestures appear somewhat stilted.

As it turns out, he didn’t actually perform in any of the videos.

Instead, the ads were made using his “digital avatar,” fueled by artificial intelligence, after he licensed his likeness to TikTok last year. Now, a version of Mr. Jacqmein is out on the internet, peddling whatever an advertiser might want him to sell as long as it complies with TikTok’s marketing guidelines.

It’s what Mr. Jacqmein signed up for, but now that he has seen his avatar out in the wild, he has regrets.

“I’m definitely not anti-A.I., and I’m not anti-TikTok,” Mr. Jacqmein said in an interview, explaining that he had been trying to build his career and thought that working with such a big platform might help. But “you really don’t know the ramifications of this,” he said.

Welcome to the rapidly shifting world of advertising in the era of generative A.I.

TikTok introduced a menu of A.I. avatars last year, to star in video ads that appear seamlessly in the app’s endless feed. Mr. Jacqmein’s likeness is one of more than a dozen that TikTok advertisers can choose from to promote their products, depending on the age, gender or ethnicity they’d like their pitch person to be.

That’s putting actors in uncharted and occasionally frustrating territory, and forcing them to reckon with the loss of control over their images.

Some were paid a relative pittance for their likenesses. So far, the project appears to be a good deal for TikTok, which is owned by the Chinese company ByteDance. The company is estimated to bring in more than $10 billion in U.S. ad revenue a year.

Mr. Jacqmein, who was a few years into a pivot to acting after a career in nursing, said he had been paid $750 and a trip to the Bay Area for the work.

He worked with an outside agency, which said it was gathering footage for avatars that would be used for advertising on TikTok for a year. Mr. Jacqmein and another actor said the agency had not mentioned that their avatars could be used on other ByteDance platforms, like its image-editing app. At the time, it seemed like a promising opportunity.

Tracy Fetter, a fine artist and occasional stand-up comedian in the Bay Area, said she had been paid less than $1,000 for the same work. Another performer spoke on the condition of anonymity because his likeness had been used in what he considered to be embarrassing ads, including for a fiber supplement targeted to gay men, in which his avatar stated certain sexual preferences. He shared documentation showing he was paid $500.

Performers do not receive royalties when businesses use their avatars.

The avatars are a free tool for businesses to use in ad campaigns on TikTok, on which advertisers can spend between $20 and thousands of dollars a day.

Mr. Jacqmein, who is now represented by an agent but was not when he agreed to work with TikTok, said he wished he had negotiated for more money or put guardrails around the products that his avatar could promote. It was hard to understand how his image might be used when he was filmed for the project last year, he said.

“The technology is evolving faster than the contracts, and they are poaching eager new actors who don’t have representation into their web of avatars,” he said.

He and other performers said the agency that they had worked with had led them to believe they would receive royalties when their avatars were used.

“In the fast-paced, ever-evolving A.I. landscape, we maintain strict oversight of our ad products and vendor relationships to protect transparency and safety,” a TikTok spokeswoman said. “When agencies fall short of our standards, we do not hesitate to end those partnerships.”

Avatars Taking Over

Digital avatars — either fabricated from scratch or generated through footage of performers — are increasingly being used in media and advertising.

Vogue, whose pages are a premier destination for models, made waves for featuring a fully A.I. model in advertisements from the Guess brand in its August issue. The company that created the A.I. model told BuzzFeed that marketing executives liked the technology for speeding up campaigns and cutting travel and permit costs.

Major tech platforms are offering sophisticated A.I. ad creation tools to businesses. Google Workspace recently promoted A.I. avatars as a tool for companies to “create polished video content — for onboarding, announcements, product explainers and more — without the cameras or coordination headache.” Google said in a statement that the presenters were A.I.-generated and that “we cast professional, represented talent to provide performances that are used in the design of the voices you hear.”

TikTok’s videos featuring avatars have small labels that say “A.I. Generated” but otherwise seem like testimonials from real people. Mr. Jacqmein is listed as “Steve” on TikTok’s ad tools and can be placed in various settings, including a bathroom, a living room or a kitchen.

TikTok executives highlighted the tools at an advertising conference in Cannes, France, in June, saying A.I. like digital avatars was particularly appealing for small businesses. Those businesses may lack the time and money for professional actors. Avatars could be easily used through TikTok’s self-service ad tools, then promoted, via ad spending, across the app.

Craig Brommers, the chief marketing officer of American Eagle, which has experimented with TikTok’s new technology, said he had gone to TikTok’s offices near Times Square in the last year and created an avatar of himself.

“All I had to do was look into a camera and talk for five to seven minutes about anything — what I ate for breakfast, what I was reading on my train ride in,” he said in June. “Then I could program ‘Craig’ to say anything I wanted to on TikTok.”

Joe Marchese, a venture capitalist and former TV network executive, said the spread of digital avatars could be “seismic for advertising.”

“Every advertiser would like to save money if they can save money,” he said, adding that brands will weigh their cost savings against any potential backlash for using A.I. models.

‘Such a Pessimist’

Ms. Fetter, the artist, saw an ad around a year ago from a production company that was looking for local comics to film as TikTok avatars. She said she had watched technology companies, particularly those from overseas, scrape and steal her paintings and data for years. She figured that someone’s using A.I. to animate an image of her was something of an inevitability.

“My thought was, ‘Well, gosh, I’ve been on social media for so long, and images of me and my artwork are out there — I might as well get paid for it before they decide not to pay anyone for it,’” Ms. Fetter, 55, said. “Even if it’s a small amount, it’s better than zero.”

Experts say the payments are low compared with ballpark rates for commercial actors. Rafael Villegas, a director at the Kim Dawson Agency, a Dallas-based modeling and talent agency, said non-represented actors often earn $300 to $1,000 for commercials. That can jump to $2,500 and more for represented actors on nonunion jobs, he said.

Creating the avatars was relatively lo-fi. The performers worked with a small Bay Area company, Polet Production, which said it had helped make around 40 avatars, using footage of the actors they filmed on smartphones. Ekaterina Poletaeva, the director who oversaw the project, said she had gathered many of the videos with the help of one assistant.

TikTok said it did not work directly with Polet Production.

To record for her avatar, Ms. Fetter drove to an apartment complex in San Bruno, Calif., three times with several outfits: some casual, a dress, and one tightly fitting set of yoga pants and a top, which the production company had requested to see how her body moved. She also did 10 self-filming sessions at home.

She has since seen “Lucy” — her avatar’s name — in ads while scrolling on TikTok.

“It’s kind of creepy to see myself talking about a tree-cutting service," Ms. Fetter said. Her participation surprised some friends — including a lawyer who told her, “I would never do that” — but she said she was comfortable with her decision and likely to renew her agreement with TikTok.

“Pretend-me is doing better than the real me in all the years of social media that I’ve been trying to do this,” she said.

Platforms Beyond TikTok

Plenty of the ads are unremarkable, and most are unlikely to cross the radar of the performers who appear in them.

But most of the performers who spoke with The New York Times expected that their avatars would be used only on TikTok, based on the agency and their agreements. They said they were surprised to learn that their contracts left room for their avatars to appear on other ByteDance properties, like the hugely popular video-editing app CapCut.

The app wasn’t named in the contract but was apparently covered under language saying the avatars could be used by “third parties.” TikTok said the contracts clearly stated their terms and conditions.

Advertisers, too, have skirted TikTok’s policies to put the avatars on other platforms. They can technically download and edit avatar videos from TikTok’s ad tools, as long as they agree to terms saying that outputs can be shared as ads only on TikTok-branded platforms, and that they will not remove or modify any watermarks. The Times found several examples of ads that used TikTok avatars outside the app and without the A.I. labeling.

Mr. Jacqmein has been startled to see his likeness in ads on Facebook, Instagram and even YouTube — where an advertiser recently appeared to violate TikTok’s terms by having his avatar promote a “male performance” supplement. YouTube removed the video after he complained.

TikTok has said it moderates ads using technology and humans. The guidelines for TikTok’s ads — which include prohibitions on sexual services, profanity, hate speech and violence — are a key assurance for potential performers that their likenesses will not be misused.

TikTok landed in hot water last year when CNN discovered that it could direct a selection of its newly released A.I. avatars to recite portions of Hitler’s “Mein Kampf.” TikTok said at the time that the issue affected a small number of users who used an “internal testing version of the tool,” rather than the tool offered to advertisers, and that if CNN had tried uploading the harmful content to TikTok, it would have been rejected for violating its policies.

Jeanne Fromer, a professor who specializes in intellectual property law at New York University’s law school and a former A.I. researcher, said it was impossible to forecast all the scenarios in which someone’s likeness could be used. But performers probably have little legal recourse if they are unhappy about how they appear, she said.

“You could have them articulate beliefs that are counter to their political or ideological beliefs, you could have them advertising goods that they think are low class or that they find abhorrent, you could have them playing a certain type of character that they wouldn’t want to play,” she said. “You have to be pretty willing to appear in most contexts.”

Lacking ‘Silver Fox’ Energy

Tarzo, an advertising technology company in Tel Aviv that has used TikTok’s avatars for marketing in the last year, found it was faster and less expensive than working with actors.

“You can A/B-test scripts, you can A/B-test presenters, and you can do that en masse and very quickly,” said Yaniv Moore, Tarzo’s chief executive. One avatar “can speak all the languages in the world.”

At times, he said, the firm has paid actors $20 to $50 to record videos for it, so using TikTok’s avatars is not necessarily stripping money from performers. But he was surprised that they didn’t receive royalties.

Mr. Moore wondered if companies would eventually stop relying on real people for avatars to avoid such issues: “Wouldn’t it naturally sort of morph into the A.I.-generated personas where no one is selling their image?”

For now, the quirks that separate the avatars from real-life actors are something of a comfort to performers.

Mr. Jacqmein said his avatar lacked his “silver fox energy,” partly because he was asked to shave his face for it. The technology, he was told, could not render his facial hair correctly at the time.