Shares of Twitter Inc (NYSE:TWTR) are down double digits this morning on concerns of user growth slowdown. Even though the social media site beat earnings expectation for the fourth quarter and increased revenue projections above analyst expectations for the first quarter, the stock is being taken to the woodshed in current trading. Investors were looking for higher monthly users than the 241 million monthly user figure that Twitter reported yesterday. For example, only 9 million worldwide users were added in the fourth quarter. The Street was expecting a figure around 247 million monthly users. Without continual expansion of the monthly user base, the impact on future ad revenues will be negative. (Image source: cnbc.com)