Author, A. A. [Screen name]. (Year, Month Day). Title of document [Format]. Retrieved from URL
Gibson, W. [GreatDismal]. (2015, July 20). Finally read a bit about Mr. Robot. How on earth did someone not manage to stop them using that title? [Tweet]. Retrieved from http://twitter.com/GreatDismal/status/623319630115766272
In-text: (Gibson, 2015)
Include the author's screen name in brackets after the author's name. If only the screen name is known, provide it without brackets.