According to a study by Nielsen Music 360, YouTube is the most popular method of listening to music for American teenagers. Radio remains the most popular medium for discovering new music, but Google's online video site is more popular than radio, iTunes and CDs when it comes to listening.
Radio still remains the biggest music discovery option, but when it comes to listening, YouTube is out in front. The study reveals that nearly 50% of teens have radio apps on their smartphones and that digital music has passed physical CDs in terms of perception of value.
This study from Nielsen is based on results from 3,000 online consumer surveys conducted in the US. This would be why YouTube drives so much traffic, and I personally have young nieces and nephews who use YouTube to stream music all the time. They're finally getting onto the bandwagon with me and Spotify, though. I think the 'fads' these days will change quicker, as music discovery applications such as Spotify become more well-known.