SAN FRANCISCO — After a three-month standoff with Microsoft Corp., Yahoo Inc. is about to square off against its shareholders.

Incensed that Yahoo rebuffed Microsoft’s last-ditch takeover offer worth $47.5 billion, investors sent its shares plunging 15% Monday, erasing about $6 billion in market value. Many are pressuring Yahoo’s board of directors to revive talks with the software giant.

Yahoo held out for $37 a share, $4 more than Microsoft’s best bid, but one major investor said Monday that shareholders would have supported a takeover at $34. Portfolio manager Gordon Crawford blamed Yahoo’s chief executive officer, Jerry Yang, for his “unrealistic” view of the company’s value for the collapse of talks.

But Yahoo’s executive team said it remained confident in its strategy to turn around the Internet pioneer, which has struggled with slowing growth and stumbled in its heated competition with Google Inc. and other players. President Susan Decker said the company planned to be a leader in the lucrative jumpy online advertising market, both in search and display. An analyst with ThinkPanmure, William Morrison, said the rebuff to Microsoft could go down as “one of the most destructive decisions for shareholder value in the history of Internet stocks.”