Why was cover boy Justin Bieber MIA from Teen Vogue's Big Bash?

Lots of hot young Hollywood stars were at Teen Vogue's annual bash on Friday night, but one VIP was MIA: Justin Bieber. Although the teen singing sensation was featured on the cover of the mag's Young Hollywood issue, he was a no-show at the soiree. Lauren Conrad, Nikki Reed, Kelly Osbourne and many more made the scene, but the Biebs didn't. How come?The night before, one event organizer was