Assuming you really want to know, I'll tell you. 4 years ago he started posting videos on youtube and youtube users (especially girls) started noticing. This one is from 3 years ago, when he was 13. It's him playing his guitar, no singing. http://www.youtube.com/user/kidrauhl#p/u/42/lXOWt524IQM
The guy who is now his manager took him and his mom to radio stations across the U.S. and he performed acoustic versions of his songs on morning shows. They started playing his music and he had thousands of fans before he even signed a recording contract. He sings songs about love that young girls (tween and teen) want to hear. He used the internet, namely Twitter and youtube, to form a bond with his fans.
I know all of that because my daughter is a fan and I took to see his movie. (A G-rated movie, I might add, which is very uncommon these days.)
As a parent, I'd much rather my daughter listen to songs about puppy love than songs about bitches and hos and evidently many other parents feel the same. He seems like a decent kid and I hope he can somehow manage to stay grounded through all of this fame and attention.