Tech's Top Turnaround Artists

By Bloomberg Rankings and Marcus Chan - 2013-10-18T00:20:24Z

Photographer by David Paul Morris/Bloomberg

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19. Marissa Mayer, Yahoo!

Before: Yahoo's total return was 5.8 percent in the two years before the company announced Marissa Mayer would be the new CEO. By comparison, the S&P 500's total return was 30.8 percent during that same period.

After: Since Mayer's appointment in July 2012, Yahoo's stock had a total return of 116.8 percent as of Oct. 11. By comparison, the S&P 500 had a total return of 29.5 percent during the same period.

Mayer has invested in product improvements to woo more users and marketers amid increased competition from Google and Facebook. Last month, Mayer said Yahoo surpassed 800 million active monthly users, an increase of about 20 percent since she arrived.

Still, big challenges remain. This week, Yahoo forecast sales that fell short of estimates as its rivals ate away at its market share. Much of the gains in Yahoo's stock has been fueled by the appreciation of the company's stake in Chinese e-commerce giant Alibaba Group Holding, say analysts.