eBay ( EBAY) kicked off the week on the wrong foot.

Shares of eBay continued to slip in afternoon trading on Monday after bearish analyst reports about the number of listings on the company's site.

The stock was recently off $1.20, or 3.9%, to $29.59, following a drop of almost 3% on Friday.

Piper Jaffray analyst Safa Rashtchy wrote that his firm's count of eBay's fourth-quarter listings suggests that they will be 8% to 11% below his estimates. Rashtchy says the shortfall in listings could cause eBay, which announces earnings on Jan. 24, to miss Wall Street revenue estimates by $50 million to $70 million.

Total listings would be in the range of 578 million to 590 million, as opposed to Piper Jaffray's prior estimate of 693 million.

Piper Jaffray also revised its 2008 revenue estimate to $8.14 billion, or about $568 million below Wall Street's consensus estimates, according to analysts surveyed by Thomson/First Call. Rashtchy wrote that fee increases announced last week that will take effect at the end of January may hurt the company. "Recent price increases are likely to be passed on to buyers, further depressing buyer activity," Rashtchy wrote. Piper Jaffray makes a market in eBay shares.

Merrill Lynch analyst Justin Post, meanwhile, wrote in a note to clients that core listings were off to a slow start for the new year. Listings were virtually flat, picking up only 0.3% compared with the year prior. And eBay's listings in Germany were down 4% year over year.

eBay continues to face mounting pressure both in the U.S. and internationally. Internet giants such as Google ( GOOG) and Yahoo! ( YHOO) are stepping up their efforts in the e-commerce space.

Google began heavily promoting its Checkout service, which enables Internet users to make purchases, this quarter. And Yahoo! has its own Stores business, which lets vendors set up online shops.

In December, eBay announced it would scrap its own Chinese Internet site in favor of playing minority partner to local Chinese firm TOM Online ( TOMO).

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