The money is gone. Either fraud (founders were skimming off the top all along), or they got hacked (and the 'hack' could have been an inside job as well). That's why they're not paying out - they don't have enough funds available. Same thing happened previously to one of the largest bitcoin exchanges[1].
[1]http://www.dailytech.com/Inside+the+MegaHack+of+Bitcoin+the+...