Microsoft's (NASDAQ:MSFT) Bing and Google (NASDAQ:GOOG) may be mortal enemies, but they're doing a great job as a tag team pummeling Yahoo! (NASDAQ:YHOO) into irrelevance.

The latest comScore data find Microsoft and Google continuing to gain market share at Yahoo!'s expense. IAC's (NASDAQ:IACI) Ask.com and the freshly liberated AOL (NYSE:AOL) also took their lumps, but Yahoo! is the one losing the biggest chunk of audience.

 

November 2009

October 2009

November 2008

Google

65.6%

65.4%

63.5%

Yahoo!

17.5%

18.0%

20.4%

Microsoft

10.3%

9.9%

8.3%

Ask.com

3.8%

3.9%

4.0%

AOL

2.8%

2.9%

3.8%

Source: comScore.

It's not a pretty place for Yahoo! to be -- going from commanding 20.4% of the market a year ago to a mere 17.5% slice today -- and it's not going to get better. If anything, Yahoo!'s share will continue to deteriorate as its search outsourcing deal with Microsoft kicks in. Why would Yahoo! regulars stick to Bing-flavored searches on Yahoo! when they can go directly to the source?

Yahoo!'s strengths in e-mail and news will help it avoid becoming the next AOL for the time being, but the fading dot-com rock star needs new tricks to avoid the inevitable slow death.

The company is also blessed with a cash-rich balance sheet, but it may not be able to buy its way out of its slump. It can't outspend Bing on marketing, and there aren't too many billion-dollar acquisitions that could turn Yahoo!'s fortunes around. Clearly the company has to do something, because stagnancy will only eat into Yahoo!'s audience with every passing month.

Do something, Yahoo! -- and do it soon.

What would it take to make Yahoo! relevant again? Let us know in the comment box below.

Google is a Motley Fool Rule Breakers recommendation. Microsoft is a Motley Fool Inside Value pick. Microsoft is a Motley Fool Options recommendation. Try any of our Foolish newsletter services, free for 30 days.

Longtime Fool contributor Rick Munarriz wonders if we'll even be using search engines 10 years from now. He does not own shares in any of the stocks in this story. Rick is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.