SAN FRANCISCO — Yahoo Inc. is hopping on the bargain-hunting bandwagon with Groupon, the Internet’s hottest discount broker, and more than a dozen other similar services.

The partnerships announced Tuesday are the latest in a series of alliances that Yahoo Inc. has forged in the past 18 months with other Internet companies. It’s part of an effort to keep people on Yahoo’s website for longer periods and bring in more ad revenue after years of listlessness.

The turnaround efforts haven’t paid off yet, leaving Yahoo vulnerable to a possible takeover attempt. Repeated published reports have asserted buyout firms that prey on out-of-favor companies have been exploring a possible Yahoo bid that might include the participation of another struggling Internet icon, AOL Inc.

Yahoo shares fell 42 cents to $16.17 during Tuesday’s afternoon trading, well below the $33 per share that the company could have gotten from Microsoft Corp. had it accepted its rival’s offer in May 2008.

Groupon, a two-year-old startup based in Chicago, has become a hot commodity by dangling special one-day deals from merchants throughout the United States. The discounts kick in after a specified number of customers sign up for an offer. Groupon makes money by taking a large cut of the sale from the participating businesses.