U.S. stocks opened lower Friday following a slew of disappointing corporate earnings on the previous trading day. Zynga shares plunged 18.07 percent to trade at 2.87 dollars per share after the opening bell. The social game services provider posted a net loss of 15.8 million U.S. dollars in the second quarter of 2013, smaller than the prior year\' s loss of 22.8 million dollars, and its quarterly revenue fell 30.6 percent to 230.7 million dollars. The company also posted a current quarter outlook far below market expectations. Expedia shares plummeted 22.49 percent to 50.38 dollars a share in early trading, after the Internet-based travel website company said late Thursday its second-quarter earnings fell 32 percent on higher costs and expenses. Moreover, Amazon.com swung to a loss of 7 million dollars, or 2 cents a share, in the second quarter, falling from a profit of 7 million dollars a year ago and defying analysts\' expectations of earning 5 cents a share. But its quarterly sales grew 22 percent to 15.70 billion dollars. Amazon shares dipped 2.25 percent to 296.56 dollars a share. However, economic data came in positive, partly offsetting the negative impact of downbeat earnings reports. The U.S. consumer sentiment index for July rose to 85.1, the highest level in six years, according to the final reading of a joint report released by Thomson Reuters and University of Michigan on Friday. Analysts polled by Bloomberg expected the index to rise to 84.0. The market wobbled in the past couple of days, as major stock indices were looking for direction and further stimulus amid a tepid second-quarter earnings season. Investors are also pausing from making big bets before next week\' s closely-watched Federal Reserve monetary policy meeting and the U.S. non-farm payroll reports for July. Shortly after the opening bell, the Dow Jones Industrial Average dipped 75.46 points, or 0.49 percent, to 15,480.15 points. The S&P 500 slid 7.48 points, or 0.44 percent, to 1,682.77 points. The Nasdaq Composite Index dropped 17.57 points, or 0.49 percent, to 3,587.62 points