By Rex Crum, MarketWatch

SAN FRANCISCO (MarketWatch) -- Tech stocks rallied Thursday, led by big gains from Facebook Inc. after the world's largest social-networking company reported quarterly results that blew past Wall Street analysts' forecasts.

Facebook (FB) shares surged 26%, to $33.37, in the wake of the company's second-quarter earnings report, which came out late Wednesday. The company said sales rose 62% from a year ago, led by growth in mobile usage, and it reported a profit of $333 million, turning around from a loss in last year's second quarter.

Analyst Ken Sena, of Evercore Partners, raised his rating on Facebook's stock to overweight from equal weight, and lifted his price target to $34 a share from $26. In a research note, Sena said Facebook's results "support the view that positive ad pricing inflection occurred in the quarter," and should help the company's share price rise in the months ahead.

Among other leading tech stocks, Qualcomm Inc. (QCOM) shares rose 4.5%, to $64.16. After Wednesday's market close, the wireless chipmaker reported upbeat fiscal third-quarter results and gave a better-than-expected fourth-quarter forecast. Qualcomm said its results were boosted by strong sales of chipsets for mobile devices.

However, Citigroup analyst Glen Yeung cut his rating on Qualcomm's stock to neutral, saying in a research note that the market for high-end smartphones is reaching a point of saturation.

Online travel site TripAdvisor Inc. (TRIP) saw its shares rise more than 14%, to $70.06, and Chinese Internet company Baidu Inc. (BIDU) was up by more than 10%, at $125.05. Both companies reported quarterly results that topped Wall Street analysts' forecasts.

Networking-equipment maker F5 Networks Inc. (FFIV) was also on the rise, as its shares climbed more than 10%, to $89.76, due to an upbeat fiscal third-quarter report and fourth-quarter outlook.

Amazon.com Inc. (AMZN), which reports second-quarter results after the close of trading, edged up by 48 cents a share to $299.20, while online social-gaming company Zynga Inc. (ZNGA) rose more than 7%, to $3.51 a share, in advance of its earnings results, also due after the market close.

Other gains came from Pandora Media Inc. (P), up 5% at $18.80 a share, as well as Yelp Inc. (YELP) and Akamai Technologies Inc. (AKAM), both of which saw their shares rise 3%.

The Nasdaq Composite Index (RIXF) rose 12 points to 3,592, while the Philadelphia Semiconductor Index (SOX) dipped into the red.

Notable losses came from computer hard disk-drive makers Western Digital Corp.(WDC) and Seagate Technology (STX). Both companies' shares fell more than 5% Thursday.

The decline were due to those companies' earnings reports. On Wednesday, Western Digital said its fiscal fourth-quarter earnings fell 44% as it shipped fewer hard drives from the same period a year ago. Seagate, which also reported results on Wednesday, gave a revenue outlook that raised concerns about the growth rate of its cloud-storage business.

Analyst Christian Schwab at Craig-Hallum cut his ratings on both Seagate and Western Digital to sell from hold following those companies' results.

Online professional-services referral company Angie's List Inc. (ANGI) fell by more than 9%, to $24.01 a share. On Wednesday, Angie's List reported second-quarter results that met analysts' forecasts. Some analysts raised concerns about Angie's List's marketing expenses continuing to rise.

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