NEW YORK (AP) — Shares of Twitter dropped in morning trading Wednesday to their lowest point since the company went public in November. Investor concern remains over the short messaging service's ability to keep adding users and keep existing users engaged.

Twitter has said it is focusing on expanding its audience and encouraging people who do use its service to use it more often. But the San Francisco company has not been expanding its user base as quickly as its investors would like.

Twitter had 255 million monthly users at March's end, up 25 percent from a year ago.

Late Tuesday the company reported first-quarter adjusted earnings and revenue that topped Wall Street expectations.

Shares of Twitter Inc. declined $5.23, or 12.3 percent, to $37.39 in morning trading. Earlier, it slipped to $37.24.