As per the latest news Hrithik Roshan joined Twitter as @iHrithik. There has been no proper verification of the fact though, except that he was being followed by hundred plus people within 2 minutes after writing his first tweet, in favor of Karan Johar’s Shahrukh Khan starrer My Name is Khan.
Here is a screenshot of Hrithik’s profile.
You can follow him at http://twitter.com/iHrithik
Update: Hrithik’s profile was confirmed by Karan Johar who has a verified account.