Start at Google, search for your topic and twitter.
Identify people and hashtags and remember:
"Begin with the user's Twitter handle in place of the author’s name. Next, place the tweet in its entirety in quotations, inserting a period after the tweet within the quotations. Include the date and time of posting, using the reader's time zone; separate the date and time with a comma and end with a period. Include the date accessed if you deem necessary."
Examples:
@tombrokaw. “SC demonstrated why all the debates are the engines of this campaign.” Twitter, 22 Jan. 2012, 3:06 a.m., twitter.com/tombrokaw/status/160996868971704320.
@PurdueWLab. “Spring break is around the corner, and all our locations will be open next week.” Twitter, 5 Mar. 2012, 12:58 p.m., twitter.com/PurdueWLab/status/176728308736737282.
Purdue Online Writing Lab: How to Cite Electronic Sources