SAN FRANCISCO--Twitter’s Sean Garrett has departed the company, less than two years after joining as its first head of communications. His exit has been followed by the resignation of VP or marketing Pam Kramer, just three months after arriving at the social networking giant.

Garrett revealed the news of his decision through a series of Tweets. He arrived at Twitter after co-founding Next Fifteen agency 463 Communications, and has built an eight-strong team at the company.

Earlier this year, Garrett and Kramer led Twitter’s search for its first PR agency, eventually appointing Edelman for a short-term project.

The departures come after Dick Costolo became Twitter CEO in late 2010, with co-founders Evan Williams and Biz Stone reducing their involvement in the company.