SAN FRANCISCO – Yahoo Inc., the Internet company exploring strategic options, said Wednesday it has appointed Scott Thompson chief executive officer, four months after firing Carol Bartz for failing to drive a turnaround.

Thompson was most recently president of EBay’s PayPal unit, Sunnyvale, Calif.-based Yahoo, the largest U.S. Web portal, said in a statement.

The new CEO will need to boost visitors to Yahoo’s sites and attract more advertisers amid competition from Google and Facebook, while dealing with strategic decisions. Yahoo has considered options including divestitures. Microsoft and private-equity firms TPG Capital and Silver Lake have signed non-disclosure agreements to help size up a possible bid, people close to the companies said last year.

“It’s probably a slight negative because I think the best outcome for Yahoo would be an all out takeover by Microsoft,” said Brett Harriss, an analyst at Gabelli & Co. in Rye, N.Y. “Hiring a new CEO makes the sale of the whole company unlikely.”

As San Jose, Calif.-based PayPal’s president, Thompson contributed to an increase of the payment service’s users to more than 100 million, helping it close in on a goal of revenue as high as $7 billion by 2013, compared with $3.4 billion in 2010.

PayPal’s services help retailers and individuals exchange funds for purchases or payments, even without a credit card. Thompson, who has run the business since January 2008, also engineered the company’s expansion to online daily deals and mobile payments.

“It’s a surprising choice,” said Ken Sena, analyst at Evercore Partners in New York. “Scott has a great track record in payments and has proven an effective executive at PayPal and has major tech chops and international experience, but as content company, which Yahoo has increasingly become, his experience is kind of lacking.”

Thompson may play a role in extracting value from Yahoo’s international assets. Aside from its main Internet portal business, Yahoo has stakes in Asian companies that some investors have said are undervalued. Yahoo holds about 40 percent of Alibaba Group Holding, China’s biggest e-commerce company. Yahoo estimated the stake was worth about $14 billion on a pretax basis in October.

Thompson’s primary focus will be on the “core business,” and he will work closely with the board on the strategic review, Chairman Roy Bostock said in the statement.