Best of 2007

21 & Under: Hottest Breakout Stars

Zac! Rihanna! Shia! Lauren! These kids aren't only the most popular, they're also the most likely to get bigger in '08. By Aaron Parsley

THE HEARTTHROB

With the worldwide sensation High School Musical 2 breaking records and his big screen debut in Hairspray, Zac Efron, 20, proved that he's going to be making girls scream for a long, long time.