brian wallace Research in Motion’s troubles just keep mounting. After a dismal earnings report last Thursday, the smartphone maker watched its stock lose a quarter of its value. Then on Monday, it lost its a digital marketing officer.

Brian Wallace, RIM’s VP of digital marketing and media, is leaving the company to take a position at rival phone manufacturer Samsung, the Wall Street Journal reported.

The news comes at a terrible time for RIM, whose Blackberry smartphone was for many years one of the most popular in the United States before losing its innovative edge and market share to Apple’s iOS and Google’s Android platforms.

It’s telling that Wallace left RIM for Samsung, which manufactures smartphones and tablets with the Android OS. Android’s market share is growing and is projected to be the world leading smartphone OS by 2015 by two major research firms. RIM’s BlackBerry OS, on the other hand, is projected by the same firms to be in fourth place, behind Microsoft’s Windows Phone 7 and Apple’s iOS.

RIM’s biggest problem right now is that the company is not pushing out any new, innovative phones. The company tried to show the market it was thinking ahead with the debut of the BlackBerry PlayBook tablet, but the company is still hobbled by sluggish sales of its flagship smartphones, delays of new products and a plummeting stock price. Time will tell if RIM can stage a legitimate comeback.