21 Under 21: Justin Bieber
No. 2: Justin Bieber
Birthdate: March 1, 1994 (age 16)
Why He's Hot: Bieber fever may have spread last year, but it exploded to a full-on pandemic in March, when the 16-year-old Canadian debuted at No. 1 on the Billboard 200 with "My World 2.0." The Biebs has been a top 10 mainstay on the chart ever since, and he's set to branch out with a book and 3D movie in the coming months. The Madison Square Garden stop of Bieber's sold-out arena tour, during which he brought out everyone from Usher to Miley Cyrus, only further proved his starpower. Frolicking beachside with Kim Kardashian didn't hurt, either.
Video Below: Justin performs "Baby" live, March 2010.