Above: Screengrab of trending chillwave on Exfm

Back in October music discovery service Exfm attempted to transform itself from a browser extension to a full fledged web service. Apparently the kids like what they’re hearing, because the site has gone from around 75,000 active users to more than 300,000. On the strength of that growth they have raised $1.5 million from their existing investor Spark Capital, more than doubling their total funding to date.

“We’re seeing a lot of opportunity as streaming music becomes more mainstream,” founder Charles Smith told VentureBeat by phone. “We’re able to pull songs from places like SoundCloud and Bandcamp using their APIs. Then we can feature the best stuff on our destination site and give our users a great chance to stumble on new music.”

Exfm began life as Extension Entertainment, a Chrome extension that followed users across the web gathering up the tracks from sites they visited and making them easy to play and share with friends. Like any good pop artists, it has been busy reinventing itself. It took the moniker Exfm, then mobile with an iOS launch last summer. This began to introduce new channels for discovery, like a Tastemaker section.

“It’s my favorite social music experience,” Spark Capital’s Bijan Sabet told VentureBeat. “Just like news often breaks first on Twitter, I’m finding new artists are emerging within the Exfm community before it hits mainstream radio.”

The funding will be used to prepare for synchronous development across the web, Android and iOS. Exfm recently hosted its first music event in partnership with bands at New York nightclub Pianos.”One of the things we’re hoping to do this year is to build out our relationships beyond the tech industry to work with the music industry as well. We realized that we have the power to drive an audience to live events and that is a powerful thing,” Smith said.