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What: Shares of SINA (NASDAQ:SINA) have plunged by as much as 16% today after the company reported earnings with soft guidance.

So what: Non-GAAP revenue in the third quarter came out to $147.7 million, which resulted in non-GAAP earnings per share of $0.17. SINA's Weibo micro-blogging service is off to a strong monetization start, with ad revenue doubling sequentially. The company began sharing revenue with developers.

Now what: Those figures were ahead of Street forecasts, but SINA's guidance left a lot to be desired. Fourth-quarter adjusted revenue is expected to be in the range of $132 million to $136 million, well short of the $152 million that analysts and investors were hoping for. Citi downgraded the stock by two notches, from buy to sell, in the wake of the results.

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