If you don't know much about Justin Bieber's rise to superstardom, James Parker provides a good primer:
How did he do it? With YouTube, that’s how. Kissed in his cradle by the witch of the Web, Justin was throwing up little promo reels by the time he was 12. Singing a Brian McKnight song into the bathroom mirror. Or sitting on some municipal steps somewhere, busking mightily about the Lord: “You’re my God and my Fa-ther!” he bellows through the legs of passersby, the wooden body of his guitar reverberating with his shouts. ...
Bieber wasn’t from the Disney factory, and he didn’t have a show on Nickelodeon, so the marketing plan was skewed toward his already established constituency in social media: lots of Facebooking and YouTubing and sugary tweets to his millions-strong Twitter army.