SAN FRANCISCO — Yahoo Inc.’s efforts to revive takeover talks with Microsoft Corp. have reached a dead end, setting the stage for the Internet pioneer to turn over a piece of its advertising platform to online search leader Google Inc.

The news disclosed today caused Yahoo shares to plunge by more than 10% as investors abandoned hope that Microsoft would renew a five-month quest to buy the Sunnyvale-based company.

Yahoo tried to renew the discussions at Microsoft’s last offer of $47.5 billion, or $33 per share, but the software maker wasn’t willing to bid that much again, according to a statement released Thursday.

The Microsoft Chief Executive, Steve Ballmer, had withdrawn his oral offer of $47.5 billion offer after the Yahoo CEO, Jerry Yang, asked for $37 per share in a May 3 meeting at a Seattle airport.

Shortly after that breakdown, Microsoft tried to convince Yahoo to sell its online search operations instead.

But Yahoo concluded that its search engine — the Internet’s second most popular behind Google — was too important to sell piecemeal.

Yahoo said Microsoft “unequivocally” rejected the notion of buying the entire company in a meeting held Sunday.

In statement, Microsoft asserted its plan involving the purchase of Yahoo’s search operations would have been worth at least $33 per share to Yahoo.

Yahoo now has to find a way to minimize the damage to its stock, which dropped $2.63, or 10.1%, to $23.52 in today’s late trading.

With Microsoft apparently out of the picture, Yahoo is turning to Google for help.

Hoping to boost its revenue, Yahoo is expected to announce a deal that will turn over a piece of its online ad platform to Google. In a two-week trial completed in April, Google demonstrated its superior technology could generate higher revenue from text-based ad links displayed alongside some of Yahoo’s search results.