Twitter on Tuesday reported 255 million monthly active users, up 5.8 percent from the previous quarter but still less than investors were expecting. The company also said viewers refreshed their "timelines" - Twitter's equivalent of Web pageviews - 157 billion times in the first quarter.

Twitter also posted quarterly revenue of $250 million, as its mobile ads drew more viewer responses. It said its advertising revenue per thousand timeline views, a metric that measures the effectiveness of its ads, nearly doubled to $1.44.

"We had a very strong first quarter. Revenue growth accelerated on a year over year basis fueled by increased engagement and user growth," said Dick Costolo, CEO of Twitter. "We also continue to rapidly increase our reach and scale. With the integration of MoPub, we now reach more than 1 billion iOS and Android users each month, making us one of the largest in-app mobile ad exchanges in the world and the only one at scale to offer native in-app advertising."