Twitter 
(twitter.com) 

Users: 1 million
Ages: 16 – 35

Background Information:

Twitter is a social networking and micro-bloggingservice that allows users to send "updates" (text-based posts, up to 140 characters long) via SMS, instant messaging, email and the Twitter Web site.

Users typically post several messages a day, usually about mundane tasks and activities. Some Twitter users post messages about meetings times and places.

“Friends” and “followers” can receive a text message, e-mail, or instant message every time a Twitter user posts a new message. According to Twitter, the number of users and messages have been doubling every three weeks during recent periods. Twitter could be used to quickly contact hundreds of people by sending just one text message.