8Tracks today launched a new iPS app that should continue to propel impressive user growth for the free online music service. With 8 million active monthly users, 8Tracks ranks as the 5th most popular online music service in the U.S. among 19-24 years olds, according to March ComScore mobile and PC data. That number falls to 6th among 18-34 years olds and 8th overall. But those are still impressive stats in a category dominated by deep pocketed players like Spotify, Pandora and iHeartRadio. 8Tracks has received just $1.5 million in funding since launching in 2008, and says they've been profitable...

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