Photographs in illustration by Geordie Wood and Scott G. Toepfer

There's a lot Jessi Smiles can do in a six­-second video. Pound Pringles. Pretend she peed her pants. Twerk on a geek at a video-game store. She can also put every guy on the Internet in his place. "For all those boys saying that I'm hot," she coos in one clip, "just wait until you see my dick."

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On a bright afternoon in her sparse Miami Beach apartment, Smiles thumbs through some recent videos on her iPhone. She's 20, tall, curvy, pretty and blond, dressed in black leggings and a blue blouse. She just finished applying makeup, and positioning a stool by a camera, so the light is just right. Her older brother Joey is collecting money for a beer-and-pizza run before she shoots a new video, which she'll shortly post to her 3 million followers. It's one of the three or four she films each week. "When people say I'm a 'celebrity' or anything like that, I hate that," she tells me, in her slight Cuban-American accent. "I just think I'm well-known on the Internet."

Smiles is famous on Vine, the latest "It" app in the constantly changing landscape of social media. Launched in January 2013 after being purchased by Twitter for a reported $30 million, Vine lets people record and share microsize video loops, six seconds or shorter. "Your grandmother's on YouTube – it's not cool," says Marcus Johns, a precocious, good-looking 20-year-old with more than 4 million followers on the app. "Vine is the thing now. Kids in our ADD generation want to express an idea and move on to the next thing."

While recognizable faces – Wiz Khalifa, Kate Upton, President Obama – have been popping up on Vine, the medium's biggest stars are these quirky nobodies who have mastered short-attention-span theater better than anyone. Vine's rigid format is deceptively difficult to get right, but it usually requires some cocktail of charm, humor and sex appeal – just the stuff that Smiles has deftly branded.

Less than a year ago, she was a cashier at a day spa, going by her real name, Jessica Vazquez. Now she's topping her old annual salary each month (though she doesn't disclose the figure, her many sponsors, such as Wendy's, pay around $3,000 for a mention in a single clip). "My whole life has done, like, 20 somersaults," she says. "It happened very fast. When you're on Vine, you become a brand. Everyone is a brand. I'm a brand, and there's nothing you can do about that."

She sounds jaded for a reason, as is clear when her ever-present mom and manager, or "momager," as Cristina Ferrero calls herself, shows Smiles a couple of newly posted Vines. In one, a woman in an orange poncho says, "Did you all know that in prison people don't like rapists? They actually rape them. Kind of funny how that works, huh?" In another, a heavyset man, also in an orange jacket, says, "Hey, your first day in there, beat the shit out of the biggest guy you can find." Then he flashes a photo of a scruffy, boy-band-cute dude and adds, "Just grab your ankles and pray."

The guy in the photo is Curtis Lepore, a top 10 Viner, and Smiles' ex-boyfriend. Last summer, they became Vine's first reality stars, courting each other so publicly it was hard to believe it wasn't staged. As their online romance unfolded in daily updates, it became the biggest story Vine had ever seen, spawning countless hashtags, video tributes and talk of a reality show. When the couple Vined their plans to meet in New York, some 2,000 screaming fans mobbed Washington Square Park to watch their first kiss. But the fairy-tale romance quickly became a nightmare. A few weeks after their high-profile meet-up, Smiles pressed charges against Lepore for allegedly raping her.

Today, he's due in court, which explains the Viners who've donned prison orange in support of Smiles. As she watches the clips on her mom's iPhone, Smiles' ordinarily sunny disposition goes dark. "I don't like this," she says, as she puts her head in her hands and groans. But when I ask her what she thinks she and Lepore had in common, she regains her composure. "Vine," she says. "That's it."

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"I am not a rapist," Curtis Lepore tells me over pizza in North Hollywood, two weeks after I visited Smiles. Dressed in jeans and a black hoodie with the words POPULAR DEMAND across his chest, and tattoos poking out from under his sleeves, the 30-year-old barely makes eye contact as he says these words. Compared to the chipper, blue-eyed pop-punk persona he projects online, he seems bitter and depressed. Even his trusty sidekick Buster Beans, the Roomba-riding Boston terrier and most popular dog on Vine, seems to notice, as he yaps for his master's attention. "OK," Lepore says as he relents and picks Buster up. "I'll hold you in my lap like a baby."

Lepore never expected this kind of notoriety. Growing up in Syracuse, New York, the son of an engineer and an optometrist's assistant, he hungered for bigger things. A hyperactive, creative kid, he won the lead in local plays and $3,000 in a costume contest for designing a robot suit with flashing lights and a spinning bow tie. "He was a goofy kid, but always a good kid," his mother, Gayle, says. "When a bully would come to the house, Curtis would always walk away." Turned off by the beer-guzzling locals, he went straight-edge as the lead singer of a hardcore band, GhostXShip, and he quit his job as a financial planner. "He was always trying to find his niche," recalls his childhood friend, Michael Ringold.

After a rift with his band, Lepore moved to L.A. in January 2013 to pursue a career in video-game graphics. But while unemployed and couch-surfing at friends' homes, he stumbled on a more compelling diversion: Vine, which had debuted that month. With its quick, easy-to-make videos, Vine drew people turned off by higher-end productions on YouTube. As Brittany Furlan, a top Viner, puts it, "I was not tech-savvy, which is why I never did YouTube. With Vine you could shoot it and edit it on your phone."

Lepore had already amassed 20,000 followers on Instagram, mostly for posting silly photos of Buster Beans. But the snappy video world of Vine felt even more like a natural fit. "I could be myself, and I could be funny," he says. With just six seconds, though, there was one big challenge. "Basically," he says with a laugh, "you have to not suck." He started with his dog, shooting a clip of Buster gnawing some grub while Lepore made "nyum nyum" chomping sounds. But it was a spoof of a scene from Jurassic Park – taking off his sunglasses in shock, then cutting to a tortoise chewing lettuce – that landed him on Vine's highly competitive popular page. "The driving thing on Vine," as Johns puts it, "is the incessant desire to be number one."

For Lepore, who had once considered himself "addicted" to World of Warcraft, scoring on Vine quickly became a new obsession. He'd spend his days plotting out his new videos, and refining his comedic bits. Though Lepore has plenty of ego, there wasn't just that at stake; there was money. Marketers wanted to exploit the millions of hard-to-reach millennial eyeballs watching Vines. "Vine is mobile first, and also about real time," says Rachel Tipograph, former director of digital and social media for the Gap, one of the first brands to come on board. "It's a wonderful place to spread news really fast."