Before starring in the Wizards of Waverly Place show, Selena Gomez starred as an extra in various other television programs, Barney & Friends being one of the more popular ones. She then auditioned for the show and got the main role, Alex who is a wannabe wizard after finding out that her parents have magical power. The show is currently in the middle of Season 2 and its popularity is increasing.
Remember last year around the same time when Hannah Montana, the TV show was starting up? The history with regard to this seems to be repeating as even though Miley Cyrus didn't become popular overnight, Selena Gomez is following up closely and who knows where her popularity will be in a year from now.