Selena Roberts, the sports columnist who left the New York Times in 2008 to write for Sports Illustrated, has left the magazine. Roberts, most famous for breaking the Alex Rodriguez/PED story in 2009 (she sparred with A-Rod after that and critics went after Roberts), left SI on Dec. 31 when her contract expired. She’s delving into new media.

“I’ve been in the corporate media world for 25  years, and I thought, ‘why not do something different and shake it up a little bit?’” she told me in a phone call last night. So Roberts founded Roopster Media Group, and she’s in the process of developing a mobile device sports app that fuses longform, original sports journalism and entertainment, among other things. “A lot of people do blogs well, and a lot of people do opinions well, and I think this will be a new and different way for readers to experience sports journalism. We’ll do deep-dive stories, short films and many other things.”

Roberts said she’s partnering with other journalists, but wouldn’t reveal their names – they haven’t left their jobs yet – and she’s going to be speaking to investors soon. There’s no timetable yet for the app to debut.

Roberts arrived at SI amid much fanfare, just a few months after Rick Reilly left SI for ESPN. Roberts was part of a 3-person rotating replacing Reilly on the famed SI backpage, and then the rotation dwindled to two, then became a hodgepodge, and nobody’s really stuck.

“At some point, you get tired of your own voice,” she said.

Terry McDonell, Editor of the Time Inc. Sports Group, sent over a statement: “Highlighted by her reporting on the abuse of performance enhancing drugs in baseball, Selena has done significant work for Sports Illustrated. She will no doubt be successful in her endeavors and everyone at Sports Illustrated wishes her the best.”

Sources tell SI Alex Rodriguez tested positive for steroids in 2003 [Feb 7, 2009 SI]