Digital music companies have plenty of reason to dive into Internet radio. Mobile advertising, vital to mobile-first radio services, improved greatly in 2013. In their latest quarters, mobile ad revenue accounted for 49% and 58% of Facebook's and Pandora's earnings, respectively. And although on-demand services like YouTube or Spotify are changing the nature of the recorded-music business, people haven't lost interest in listening to radio. A recent Edison Research survey says 53% of online Americans ages 12 and older are Internet radio users.