Not surprisingly, Twitter will continue to expand its PR team, says vice president of communications Sean Garrett, who joined the company as its first internal PR person this past March.

Garrett has staffed up recently, hiring Carolyn Penner from Google and Matt Graves from social music service imeem.

Now the company is looking for a government liaison in Washington, D.C. to lead up what it calls a “fledgling public policy department.” In addition, the company will also add two to three PR positions before the end of 2010, reports PRWeek.

Tim Dyson, CEO of Next Fifteen Communications, the holding company of Garrett’s previously employer, 463 Communications, recently told PRNewser that he believes Garrett’s job is “awfully challenging,” given his amount of resources in relation to Twitter’s growth and communications demands being put on the company.

Matt Graves, formerly head of marketing communications at social music service imeem, has joined Twitter’s growing PR department. imeem was acquired by MySpace in November 2009 and subsequently shut down.

Before imeem, Graves was director of public relations at RealNetworks.

463 Communications Partner Sean Garrett joined Twitter as the company’s first internal PR executive — with the title vp of communications — this past February. His first hire was Carolyn Penner from Google in April.

“I’m looking to hire two relatively senior people and one junior person. I am not looking to hire an agency anytime soon,” Garrett told PRNewser in March.

First on PRNewser: Twitter has hired Carolyn Penner from Google to join its growing PR team, Twitter VP Communications Sean Garrett confirmed to PRNewser today.

Penner has been with Google for almost three years and most recently held the position of associate in the global communications and public affairs department.

Garrett told PRNewser Penner starts with the company next week. Garrett himself joined Twitter in mid-February and told PRNewser that he plans on expanding his team.