Facebook shares extended their slump Tuesday after a much-hyped public offering earlier this month, shedding more than seven percent as markets reopened following a US holiday weekend. In midday trade, Facebook slid 7.4 percent at $29.56, or down more than 20 percent from its offering price of $38 on May 18. The market action came amid reports that Facebook was preparing to launch its own mobile phone, apparently as part of a strategy to get more revenues from the mobile space. Another report last week said Facebook was considering the acquisition of Opera, the Norwegian-based maker of browser software that is widely used on mobile devices. A series of lawsuits have been filed against Facebook and its underwriters claiming key information about the company\'s outlook was withheld from investors ahead of the IPO.