Jerry Yang, the founder of Yahoo, is leaving the company that he founded in his university dorm room 17 years ago, it was announced last night.

The departure of its talismanic founder comes as Yahoo examines big changes to its strategy, in the wake of its declining influence and poor share-price performance. Mr Yang is "a visionary and a pioneer", the company's chairman Roy Bostock said in a glowing tribute. But the departure was cheered by the stock market, which sent Yahoo shares up almost 4 per cent in after-hours trading.

Speculators are betting that Mr Yang's exit paves the way for a restructuring or even a sale of the company. Rebel shareholders have been calling for board changes, claiming that current directors – Mr Yang and Mr Bostock in particular – have stood in the way of changes that would unlock shareholder value.

Yahoo began life as "Jerry and David's Guide to the World Wide Web" when it was created by Mr Yang and his Stanford University friend David Filo in 1994. It grew into one of the most important gateways to the internet for 700 million users, spanning websites, search engines and email. But its power and profitability has been eclipsed by Google and, more recently, Facebook.

Earlier this month, Yahoo appointed a new chief executive, Scott Thompson from PayPal, and it has been entertaining bids for a minority stake in the company from at least two consortiums of investors, including private-equity firms and Yahoo's rival, Microsoft.

Mr Yang said: "My time at Yahoo, from its founding to the present, has encompassed some of the most exciting and rewarding experiences of my life. However, the time has come for me to pursue other interests."