By Julia Boorstin , CNBC Correspondent NEW YORK ( CNBC) -- Pinterest hit 10 million monthly unique visitors faster than any other website, drawing comparisons to Facebook. But now growth of the service for sharing images from across the web in "virtual scrapbooks" is coming back to earth. Data through March 18th which Comscore shared exclusively with CNBC reveal that the company's growth has started to slow this month. The technical details: a four week moving average of Pinterest's unique users showed that growth slowed from an 85% rate between mid-January and mid-February, to an 18% rate between mid-February and mid-March. Based on the latest data Comscore projects that Pinterest will grow its total unique users in March to just over 20 million, just a roughly 12% month-over month increase, after posting a 50% increase in February.
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