Microblogging service Twitter has tapped a former Google Inc executive to be its chief operating officer, the latest move by the fledgling but fast-growing company to build out its management team as it seeks to start making money.

Dick Costolo will join Twitter next week as COO, company spokeswoman Jenna Sampson said by email.

Twitter, which allows users to broadcast short, 140-character text messages over the Internet to groups of followers, is one of the Internet's fastest growing companies.

The number of worldwide unique visitors to the Twitter website reached 44.5 million in June, up 15-fold year-over-year, according to comScore data.

Twitter co-Founder Biz Stone said in May that the company is exploring ways to generate revenue from its free service this year, citing analytics tools and a directory of authenticated commercial accounts as potential money makers.

In January, Twitter announced that it had hired a director of mobile business development.

Costolo, who could not be reached for comment, was previously the CEO of Feedburner, which Google acquired in 2007. A profile on Costolo's LinkedIn page said that he worked at Google as a group product manager until June 2009.

(Reporting by Alexei Oreskovic; Editing by Gary Hill)