As it happens, a rabidly obsessed following of teenagers is valuable to advertisers. And so on Wednesday night, YouTube (GOOG) smartly put those teenagers on display for a crowd of 2,400 besuited advertisers at its NewFront ad sales event. Teens filled the first several rows of the Madison Square Garden presentation, adding a massive helping of “Woooooo”s to just about everything YouTube CEO Susan Wojicki said.

“The number of people visiting Youtube is up by 40% year on year,” she declared. Wooooo!

“Watch time is growing by 50% year on year.” Wooooo!

“YouTube reaches more 18 to 49 year olds on mobile alone than any cable network.” Wooooo!

“Fans,”Wojicki quipped, “feel free to do that whenever I say anything, at all.” Wooooo!

Given how dry and awkward these corporate pitch events can be, the cheering added a refreshing element of liveliness. A performance from a breakdancing troupe helped, as did comedy from Grace Helbig and musical performances from a Harlem Gospel Choir, Nate Ruess, Bruno Mars, and Mark Ronson. (At one point, sirens wailed and two men in firefighter gear walked onstage to spray fire extinguishers on Mars’ feet as he danced.)

In addition to the ad sales pitch, the NewFront event was a celebration of YouTube’s 10th birthday. Not celebrated: The fast arrival of new streaming video competitors. For the first 10 years of its life, YouTube was the only online video game in town. With one billion monthly active users, no other platform could compete with YouTube’s scale.

But in the last year, that has changed. Facebook video became huge overnight—the company last week announced it now serves 4 billion video streams per month. Vessel, a new startup with $132.5 million in venture funding, is attempting to lure YouTube stars to its platform. Snapchat Discover is providing as many as 1 million streams per video for some of its media partners. The video category is getting crowded.

Meanwhile, questions have swirled around whether YouTube can make real money. The service reportedly earns $4 billion in annual revenue but is not profitable. Parent company Google (GOOG) touted YouTube in its earnings call last week, with business chief Omid Kordestani using the well-trod startup line that YouTube could be profitable right now if it wanted to.

But a NewFront program is not the place to address profitability or competition. At last night’s event, YouTube instead played up its stars and its cultural impact, with a highlights reel that spanned Justin Bieber, Malala, Gangnam Style and Hilary Clinton’s presidential campaign announcement. One attendee noted that, in terms of polish and star power, the event was almost indistinguishable from a TV Upfront.

That is, until John Green, a novelist and YouTube star, took the stage with an unusual sales tactic.

“I am not here to kiss up to you,” he declared. “I’m here to scare you.” He presented an ominous “vision of what will happen” to advertisers who don’t spend on YouTube.

“There is a great and terrible feeling that our lives and work is meaningless, and CSI: Miami is incredibly good at distracting us from that feeling,” Green said, noting that he was not joking when the audience chuckled. Television, he warned, is merely a distraction from “the darkness which is you.”

Unlike TV, YouTube is not in the distraction business, he continued. No, YouTube is in the community business. Advertising on YouTube helps build those communities, which is good for those communities, and for YouTube creators, and for YouTube, and “finally, coincidentally” it’s good for brands too.

The audience of ad executives did not erupt in a “Woooooo!” at this statement, but the teens in the front dutifully cheered.

At the after party, ad execs posed in a Slow Mo Guys photobooth and danced to a DJ set from Snoop Dogg. Outside, a gaggle of teenage girls in crop tops and platform sneakers lingered, hoping to catch a glimpse of Tyler Oakley or Dude Perfect. “It looks so fun in there,” one said with a sigh.