Barely a week after Twitter released its #music application, the executive who spearheaded the product resigned to join a mystery startup, according to a report on AllThingsD

Kevin Thau, who had championed Twitter's acquisition of a small developer called We Are Hunted and used their technology to form the kernel of #music, is reportedly leaving to join a company started by Twitter co-founder Biz Stone. That company, called Jelly Industries Inc., has also snagged other top Twitter executives, including Ben Finkel who headed up New User Experience on Twitter's Growth Team and is a Jelly co-founder. The San Francisco-based startup is currently in "stealth mode" and has not announced its product or mission.

With Thau reportedly out the door, that leaves newcomers Stephen Phillips, Richard Slatter and Michael Doherty from We Are Hunted as the most visible executives in charge of Twitter #music. The tiny company recently moved its operations from Australia, where it was founded, to San Francisco following its acquisition.

The company did not immediately respond to a request for comment. The app, which functions separately from the core Twitter microblogging platform, lets users follow artists they're interested in, listen to their music via Spotify or Rdio and buy their music through iTunes. Twitter is also in negotiations with Vevo to add music videos.

Twitter's music application debuted last week as an iOS and Web application. As of Wednesday evening, it was the 13th most downloaded free application on iTunes overall and the top free music application. Twitter's video blogging app, Vine, was the top free app overall on iTunes. 

Between Vine and #music, Twitter has the beginnings of a multi-media social platform that allows the company to diversify from its self-imposed 140-character Tweet limitations and branch out into richer forms of media advertising. The company is reportedly working to pull together deals with TV and film studios to distribute richer video content, either as a second-screen play or as a standalone application.