Sixteen-year-old Keenan Cahill has overcome a rare genetic disorder to become an internet superstar for his hilarious lip-synching of hit songs. He even has his own Youtube channel! It started as a hobby, but when Katy Perry saw his version of "Teenage Dream," it went to a whole new level -- celebrities ranging from rappers to pro athletes have even joined him in his latest videos. Check out the one (which has nearly 38 million views, BTW) that launched Keenan's career into the stratosphere.