JUSTIN BIEBER began posting videos of himself singing on YouTube when he was only twelve. By the time he was fifteen, his YouTube channel had over a million views and he caught the attention of a music executive. Signed to a major label (Island Records) in 2008, Bieber is now a certified sensation, with multiple hit songs and legions of teenage female fans, who have caused at least three stampedes at various appearances. ChinaFotoPress/ChinaFotoPress via Getty Images