9. Cody Simpson: 21 Under 21 (2013)
Last Year's Rank: 12
Birthdate: January 11, 1997 (Age 16)
Why He's Hot: Cody Simpson's career has steadily gained momentum since he was discovered on YouTube in 2009. Likewise, the Scooter Braun client has risen in each of the past three years on Billboard's 21 Under 21, from 20 to 15, then to 12 last year, and this year to 9. At the tender age of 16, this Australian shows no signs of slowing down. This year's mini album "Surfer's Paradise" marked his highest debut yet on the Billboard 200 (No. 10) and its lead single "Pretty Brown Eyes" spent 5 weeks on Pop Songs, peaking at No. 34. And rocking the handsome, blonde-haired surfer dude look doesn't hurt, either.