For her 18th birthday in March, “Jacky Dejo,” a snowboarder, bikini model and child influencer turned social media entrepreneur, celebrated on the secluded island of Dominica.

On Instagram, she appeared in strappy swimsuits, basking luxuriously on a black-sand beach and floating in a jungle stream.

Her fans — thousands of men had been following her through her teens as she posted and sold photos — wished her well and eagerly anticipated her next move online as an adult.

“Happy birthday,” one wrote in French. “I can’t wait to see you without any clothes on.”

Born two years after the launch of Facebook, she belongs to the first generation to grow up with social media and the multibillion-dollar creator economy that is redefining adolescence for girls.

A Dutch citizen — her real name is Jacquelina de Jong — she has lived in more than a half-dozen countries and picks up languages with ease. But she is equally at home on the internet, where she has built a global fan base that is dominated by American men. At 16, with the consent of her parents, she was pulling in upward of $50,000 some months, she says, charging for access to her online posts and images.

When The New York Times began investigating the culture of underage girl influencers more than a year ago, Jacky Dejo — or simply Jacky, as she is widely known by her followers on the internet — quickly emerged as a prominent and enigmatic figure.