No. 8. Nick Jonas
Birthdate: Sept. 16, 1992 (Age 19)
Why He's Hot: The JoBros may be on indefinite hiatus, but that hasn't done anything to slow the roll of the group's youngest member. In early 2010, Nick became the first Jonas brother to release a major album separate from the platinum-selling trio. "Who I Am," by Nick and his band The Administration, debuted at No. 3 on the Billboard 200. Nick has continued to flex his songwriting muscles - working with fellow 21-Under-21 artist Greyson Chance, among others - and has also ventured back to the theater stage, where he first got his start. Nick played the role of Link Larkin in thr broadway production of 'Hairspray' in August 2011 and will return to the Great White Way in 2012 when he stars as J. Pierrepont Finch in the musical "How to Succeed in Business Without Really Trying."