Gavin Doyle used allowance money in 2009, when he was 11, to buy a few shares of Disney stock. They cost $31 apiece.

He now owns a little over 400 shares — barely enough to be a speck of dust in the Disney investor galaxy. But the entertainment company, which has 1.8 billion shares outstanding, has nonetheless barraged him for months with political-style campaign materials (letters, email, social media ads) that urge him to elect certain people to its board.

“I guess every vote matters,” said Mr. Doyle, 26, who runs MickeyVisit, a blog unaffiliated with Disney that focuses on theme park vacation planning.

In most cases, global companies pay little attention to individual shareholders. Powerful institutional investors like mutual funds and index funds typically run the show. But Disney finds itself in an atypical situation as it scrambles to thwart Nelson Peltz, an activist investor who is seeking two board seats, including one for himself.

Up to 40 percent of Disney shares are held by individuals — retail investors, as Wall Street sometimes refers to them, with a hint of derision. On average among public companies, individuals represent closer to 15 percent of the ownership, according to analysts and academic studies.

“In the retail market, a lot of individuals don’t feel comfortable investing in companies they’ve never heard of,” said David Reibstein, a professor at the Wharton School at the University of Pennsylvania. “Disney is known: I can relate to it, I have taken my kids there, I’ve seen their movies.”