Twitter investors disappointed over modest increase in active users

SAN FRANCISCO (Reuters) - Twitter Inc on Tuesday reported 255 million monthly active users, up 5.8 percent from the previous quarter but not enough to satisfy investors increasingly concerned about its struggle to gain a mass following.

Its shares fell 8.5 percent to $39 in extended trading.

The San Francisco-based company also said viewers refreshed their "timelines" - Twitter's equivalent of Web pageviews - 157 billion times in the first quarter, slightly below what some analysts had hoped for.

The company, however, posted better-than-expected quarterly revenue of $250 million, as its mobile ads drew more viewer responses.

Twitter Chief Executive Dick Costolo pledged in February to revive user growth after disclosing it had fallen to its lowest rate in years. Its shares have been trading 40 percent below their peak as investors wait to see whether the service could broaden its appeal.

(Reporting by Gerry Shih; Editing by David Gregorio)

[Image via Agence France-Presse]