While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Weibo Corp. (NASDAQ:WB) rallied 2% today after Goldman Sachs initiated coverage on the Chinese social media coverage with a buy rating.

So what: Along with the bullish call, analyst Piyush Mubayi planted a price target of $24 on the stock, representing about 23% worth of upside to yesterday's close. So while momentum traders might be turned off by Weibo's price weakness in recent weeks, Mubayi's call could reflect a sense on Wall Street that its growth prospects are becoming too cheap to pass up.

Now what: According to Goldman, Weibo's risk/reward trade-off is rather attractive at this point. "Weibo attracts a broad range of content that in turn attracts a growing number of users and content providers, driving a virtuous cycle that reinforces its position as China's leading social media platform," said Mubayi. "Revenue visibility is supported by major stakeholders Sina (through which it transacts with advertisers) and Alibaba (with which the company expects to generate US$380 mn in ad revenues over 2013-2015). ... We believe Weibo offers attractive exposure to the growing mobile Internet market." Given Weibo's still-speculative nature and forward P/E in the high-70s, however, I'd hold out for a much wider margin of safety before buying into that bullishness. 

Brian Pacampara has no position in any stocks mentioned, and neither does The Motley Fool. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.