(Telecompaper) Daily deals site Groupon's co-founder and CEO, Andrew Mason, has announced in an e-mail to staff that he was fired. Mason wrote that he was leaving because he was accountable for the performance of the company which missed its targets for two quarters and saw its stock price fall to around a quarter of its listing price. Co-founder and chairman Eric Lefkofsky and vice chairman Ted Leonsis will run Groupon while they look for a new CEO. A Groupon spokesman told Reuters that an outside firm would be hired to find a successor for Mason. The board will consider internal and internal candidates. B Riley analyst Sameet Sinha said that one of the strongest internal candidates was Groupon COO Kal Raman, formerly at Ebay and Amazon.