Today (March 1), Beliebers, as fans of pop star Justin Bieber prefer to call themselves, celebrate the singer's 28th birthday. With the release of his debut mini-album 'My World' in 2009, the singer and songwriter became a teen phenomenon. Bieber has released five albums since then, including 'My World 2.0', 'Under the Mistletoe', 'Believe', 'Purpose', and 'Changes'. From 'Baby' to 'Yummy,' here are some of the highest-grossing songs by the artist: