6. Austin Mahone: 21 Under 21 (2014)

Tawni Bannister
Austin Mahone photographed backstage at the Billboard+Twitter Music Chart Launch on May 28, 2014.

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Birthdate: April 4, 1996 (Age: 18)

Last Year's Rank: 7

Why He's Hot: Austin Mahone, the heir presumptive to the teen-pop throne Justin Bieber seems all too eager to abdicate, continued to ascend this year. As his signing to Young Money Cash Money Billionaires late last year indicated, Mahone -- who now resides on the same label as Lil Wayne, Drake and Nicki Minaj -- is more than just a clean-cut heartthrob in waiting. His second EP, The Secret, reached No. 5 on the Billboard 200, and Mahone became the first artist to top the Billboard Twitter 140 chart, proving the strength of his solid fanbase of 7 million Twitter followers. While a fever and a blood clot forced him to move his MTV Artist to Watch tour from this fall to 2015, the Mahomie support that flooded Twitter after news of his hospitalization -- and his top 20 standing on the Billboard Social 50 -- is proof of his fans’ allegiance.

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Billboard's 2014 21 Under 21 List