More than an hour before the doors open at the Anaheim Convention Center, there's already a line that stretches from the entrance, past a nearby Hilton, around a water fountain, through a palm-tree lined promenade, and all the way to the driveway's entrance. Security guards in yellow shirts have begun packing people into neat zig-zag rows so that they do not spill out onto the street. "I'm seeing these damn tweens in my nightmares," one of them will tell me the next day, shaking his head like he's trying to dislodge an unpleasant memory. "I've worked Justin Bieber concerts. This is the same thing."

A colorful mash of backpacks, shorts, and Converse sneakers, the line is comprised mostly of groggy teenagers, who sit on the ground in circles, clutching water bottles, bags of Doritos, iPhones, and playing cards. Nothing about it seems nightmare-inducing.

That is, until a high-pitched scream slices through the quiet morning.

It spreads like a virus. "Oh my god, oh my god," girls suddenly chant in unison, their hands quivering by their faces in disbelief. Entering the building is a man in his thirties wearing a striped hoodie and jeans. I search for a teenage heartthrob, or a movie star, but the screaming is for him. He waves both of his hands and smiles before ducking inside.

Girls nearby soon inform me he is Hank Green, who along with his brother, John, founded VidCon five years ago. The screaming teenagers, who are here to attend the "world's premier gathering of people who make online video," recognize Green from vlogs the brothers post to their shared YouTube channel. And their success extends offline. Recently John's best-selling novel, The Fault In Our Stars, was turned into a movie that beat Tom Cruise's sci-fi thriller, Edge of Tomorrow, on opening weekend at the box office.

The rise of YouTube as a distribution channel is creating a new genre of fame that looks less like Tom Cruise than it does John and Hank Green–a shift that baffles just about everybody older than 18, including Hank Green. "I want to tell you a secret," he will explain later during a keynote speech. "I don't know what I'm doing. I have no idea. I don't think that any of us know what we're doing. There is a wave, and it's made of technological things and sociological things, and it's individual people making individual decisions about how they're going to spend their individual time. And we are riding it. And that's impressive. But it is not as impressive as understanding the wave."

Executives from entertainment companies, talent agencies, video startups, and, yes, YouTube itself, have come to VidCon with hopes of gaining that understanding. They have been let into the conference center early, and though none of them is old, per se, their accoutrements betray their age. Laptops, briefcases, coffee, and an occasional suit jacket separate them from the line outside far more than the wall of glass doors.

These "industry" badge-holders will spend the next several days on the third floor of the convention center–attending panels with titles like "Working With the Next Generation Of Talent" and listening to keynotes by industry leaders like DreamWorks Animation CEO Jeffrey Katzenberg–in an effort to decipher what is happening on the first floor. Most of them cannot reasonably blend in to a crowd of teenage girls. But I can. As the security guards visibly brace themselves for the doors to open, I tug on the straps of my baby blue backpack, adjust my ponytail, and prepare to enter the crazed world of YouTube fandom on the level where it lives.

A sea of girls is hoisting cell phones into the air. It's impossible to tell whether it's a line or whether there's something extremely interesting toward the center of the mob. A scream erupts from a far corner. "What's happening?" I ask a tall blonde girl next to me. "I don't know. Someone came out," she says.

I wander over to the next group and poke my head into their circle for clarification. "Hey, is this a line?" I ask. It is a line–a line to get into other lines that will lead to specific YouTubers' autograph signing booths once they open (the word is "YouTubers," by the way, not "YouTube celebrities" or "YouTube stars").

"Who are you here to see?" one girl asks. Nobody in particular, I tell her, you? "The British YouTubers."

Who? There are enough successful YouTubers that it would be impossible to know every star, and one person's hero can be, to another teenager, a total unknown. "You know, Jim Chapman, Alfie Deyes, Joe Sugg, Caspar Lee, Marcus Butler," the girl says. I don't know, and my blank expression is met with exasperated disbelief. It's time to move on.

As I bump around the crowd trying to figure out where the line starts, I learn that "Who are you here to see?" is the question at this conference in the way that "Where do you work?" might be the question at a professional networking event.

Some kids are here to see beauty vloggers like Michelle Phan (6.7 million subscribers), who posts tutorials about makeup and life advice on her channel. Another, typically older, crowd prefers the Jon Stewart-esque commentary of Philip DeFranco (3.3 million subscribers) and the news-based comedy channel he created called SourceFed (1.4 million subscribers). Others enjoy following daily updates from a family of six that goes by the name "Shaytards" (2.4 million subscribers). The Fine Brothers (9.3 million subscribers), who mostly direct rather than star in videos on their channel, attract an audience that is half comprised of people older than 25, though you'd never guess it here. Other corners of YouTube, like the extremely popular video game YouTubers, aren't even represented at VidCon, where teenage girls running after cute boy YouTubers are the most visible force.