“He causes riots everywhere he goes, and my Mom loves him almost as much as I do!” sputters a blonde girl in a bubble-gum pink sweater, flanked by two other breathless tweens. You’d have to be on a serious pop-culture fast not to know which star they’re kvelling over, but in any event, they let his name be heard-loudly. “Justin Bieeeberrr!”

Photos: Justin Bieber Lets His Fingers Do the Talking

Sleepy-eyed before, the crowd perks up. Not to the point of full-on “Biebermania” or anything. It is, after all, 10 o’clock on a Thursday morning, and of the hundreds packed into New York’s Hammerstein Ballroom, roughly three dozen are kids who’ve managed to score VIP seats before taking their SATs. Bieber is performing at Nickelodeon’s 2010 upfront presentation, where the youth-centric network is announcing its new slate of programming. After sitting attentively through pitches about “igniting fan position” and supercharging the SpongeBob SquarePants franchise, suited-up ad execs and tastemakers now hover curiously over their seats, necks craned, phones and Flip cams in hand, angling to grab a snippet of the most famous 16-year-old in the game.

“Your world is my world, and my heart is your heart,” Bieber sings in a sweet tenor, perched on a stool and strumming the melody of his first hit, “One Time,” on an acoustic guitar. Then he launches into his new single, “Baby,” bounding through choreography, thwacking his drummer’s kit, rapping Ludacris’ guest verse and clutching his chest during swoon-worthy lines like, “We will nevah-evah-evah be apart.” Afterward, Bieber sticks around to change the lives of a few brace-faced girls, who are hugging the lip of the stage and clutching their Converse in the hopes of an autograph.

“He-signed-my-shoes-and-my-arm-and-my-cell-phone,” says Stephanie Mordoh, a breathless eighth grader from Westchester who’s there with two friends. “He’s just so talented and amazing.” Bieber takes a few photos and on-camera questions. On the Jonas Brothers vs. Justin Bieber inter-fan beef (their shared initials are partly responsible, as anyone under 16 will tell you), he calmly says, “Our fans seem to fight and I don’t know why. But I don’t care, you know? It’s whatever.” Five minutes later, he’s gone, whisked away by his handlers to the next appearance.

Since being plucked from his hometown of Stratford, Ontario, Bieber has grown from a 13-year-old with a popular YouTube account into a Taylor Swift-co-signed sensation, boasting sales and social-network stats that rival those of any Disney star. The difference between him and Miley Cyrus or the Jonas Brothers, though, is that their careers were jump-started by TV shows.

“There are other artists who have platforms and then get to the musical space, and where that goes, no one really knows,” Island Records president Steve Bartels says. “Yes, Justin is a phenom, but it’s really backed up. He’s got that viral cachet right now, but what he stands for at the end of the day is music. We’re keeping our fingers crossed, obviously, but we think we have something here that has incredible longevity.”

Bieber’s debut album, “My World,” was released last November on Island through the Raymond Braun Music Group (a 50/50 joint venture between R&B star Usher Raymond and Bieber’s manager, Scott “Scooter” Braun). It arrived at No. 6 on the Billboard 200 with 137,000 copies and has since sold 998,000, according to Nielsen SoundScan, a total likely boosted by iTunes’ Complete My Album campaign. Four tracks-”One Time,” “One Less Lonely Girl,” “Favorite Girl” and “Love Me”-were released prior to the album’s street date and have all charted, making Bieber the first solo artist to have four top 40 singles before the release of his debut album. All seven of the album’s songs have charted since, adding up to 3.3 million in individual track sales.