U.S. stocks extended losses in midday Friday as a slew of disappointing corporate earnings on the previous trading day offset positive consumer sentiment data. The Dow and the S&P 500 are on track for their first weekly decline in five weeks. Zynga shares plunged 16.57 percent to trade at 2.92 dollars per share in midday Friday. 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 24.77 percent to trade at 48.90 dollars a share, 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 reversed early losses, gaining 1.45 percent to 307.81 dollars a share in midday. On the positive side, Starbucks\' quarterly revenues climbed 13 percent to 3.74 billion dollars. Shares of the coffee chain jumped 6.47 percent to 72.58 dollars a share in midday. According to Thomson Reuters data, 47 percent of the S&P 500 companies have reported second-quarter earnings so far, among which some 68 percent have beaten profit estimates, while some 56 percent have topped revenue forecast. Economic data came in favorably but failed to offset 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 lackluster second-quarter earnings season. Investors become cautious of placing big bets before next week\'s closely-watched Federal Reserve monetary policy meeting and the U.S. non-farm payroll reports for July. In midday trading, the Dow Jones Industrial Average plunged 105. 87 points, or 0.68 percent, to 15,449.74 points. The S&P 500 slid 8.71 points, or 0.52 percent, to 1,681.54 points. The Nasdaq Composite Index dropped 9.77 points, or 0.27 percent, to 3,595.42 points.