3. Miley Cyrus: 21 Under 21 (2013)
Last Year's Rank: 18
Birthdate: November 23, 1992 (age 20)
Why She's Hot: On last year's 21 Under 21 list, Miley Cyrus was ranked at No. 18, and we argued, "Miley Cyrus' musical career has been quiet this year, but that's looking to change in 2013." Boy, did it ever. After her 2010 album "Can't Be Tamed" debuted at No. 3 on the Billboard 200 chart but failed to spawn an overpoweringly hot single, Cyrus regrouped, chopped off her locks, linked up with new collaborators and returned with a fresh, hip-hop-inflected sound. The Mike WiLL Made It-produced "We Can't Stop" served as a summer-appropriate comeback single and presented the most unforgettable moment at this year's MTV Video Music Awards, but "Wrecking Ball" was an even bigger smash (pun intended), and gave Cyrus her first No. 1 single on the Hot 100 chart. With "SNL," a TV documentary and lots more twerking in her immediate future, the sky is the limit for the former Hannah Montana on the eve of her 21st birthday.