That may seem like an exaggeration, but when I took a walk with him around Union Square last week, he was stopped every few feet by squealing teenagers who begged to take a selfie with the 6-foot-3 Frenchman. Some girls were brought to tears; others proclaimed they “couldn’t breathe” at the mere sight of him. During one loop around the park, he was stopped more than 50 times.

What makes Mr. Jarre so loved by his fans (he likes to call them “friends,” saying that “fans” sounds too hierarchical) is that he is relentlessly positive. There is rarely a photo or video of him in which he is not grinning from ear to ear. The messages he espouses — sometimes in videos, other times in all caps — are meant to inspire kids who have been bullied or are insecure.

“Spend your life doing strange things with weird people,” he wrote last week on Twitter. In another tweet he said, “The best way to multiply your happiness is to share it with others.”

While these missives may seem quixotic to adults, teenagers eat them up. During one of our meetings, Alexis, a young teenager with mismatched socks and pink hair, ran up to Mr. Jarre and begged him to go to prom with her. “I look up to him in every way, shape and form,” she told me. “He’s my best friend.” The wallpaper on her smartphone was a quote from him.

Mr. Jarre is used to this by now, but the level of fame still surprises him. When he visited Iceland last year with another Vine star, Nash Grier, the two sent a note on social media saying they would pose for pictures at the Smaralind shopping mall. When they arrived, the mall was overrun with more than 6,000 teenagers. The sole security guard on duty thought the mall was under a bizarre terrorist attack.