By Rex Crum, MarketWatch

SAN FRANCISCO (MarketWatch) -- Big losses from Twitter Inc. and eBay Inc. dragged on the tech sector Wednesday as investors turned against the Internet bellwethers due to certain aspects of concern in the those companies' quarterly earnings reports.

Twitter (TWTR) shares fell more than 12%, to $37.49 after the social-networking leader reported late Tuesday that its first-quarter revenue nearly doubled from a year ago, to $250.5 million. Twitter also said it broke even on a per-share basis, excluding one-time items. Analysts surveyed by FactSet had forecast Twitter to lose 3 cents a share on $241.5 million in sales.

However, it was Twitter's user-growth rates that hit the company's stock price Wednesday. Twitter said it had 255 million average monthly active users at the end of March, while analysts had been forecasting 257 million such users.

EBay (EBAY) also took it on the chin, as its shares fell 6% to $51.29. On Tuesday, the e-commerce leader reported first-quarter earnings, excluding one-time items, of 70 cents a share on revenue of $4.26 billion. Those results topped the forecasts of analysts, who were looking for eBay to earn 67 cents a share on $4.22 billion sales.

However, eBay's second-quarter outlook failed to inspire the market. And even though eBay's PayPal unit performed well, more concerns were raised about growth in the company's marketplaces business and in eBay's overall U.S. operations.

"While PayPal's performance was strong across the board, marketplaces results were light, particularly [with] margins and U.S. gross marketplace value growth," said Bernstein Research analyst Carlos Kirjner.

Other declines came from Yelp Inc. (YELP), which was off by 4.5% in advance of its first-quarter results, due after the close of trading, as well as Yahoo Inc. (YHOO), Pandora Media Inc. (P) and Netflix Inc. (NFLX).

Advancers included Apple Inc. (AAPL), Amazon.com Inc. (AMZN) and IBM Corp. (IBM).

The Nasdaq Composite Index (RIXF) looked to be headed for an erratic market session, as it remained down by 6 points at 4,096. The Philadelphia Semiconductor Index (SOX) managed to edge into positive territory.

More tech news from MarketWatch:

Twitter's dilemma: "User growth a canary"

Why teens are rebelling against Facebook

Allianz says look at Internet, biotech for next Apple

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