Robert Downey Jr. has joined Twitter.

The 'Iron Man' star posted his first tweet on Friday afternoon (11.04.14) and amassed almost one million followers in less than 24 hours.

The 49-year-old actor made his debut on the social networking site by sharing a photograph of himself wearing sunglasses and holding a sign bearing his new verified Twitter handle @RobertDowneyJr, captioned: ''Talk to me, Twitter''

After encouraging his fans to get in touch, he admitted he was still struggling to get to grips with the platform, writing: ''Loving all the love, folks. It's been a blast. Though can somebody please explain how anyone can keep their thoughts to 140 characters or le (sic)''

The actor, whose short bio simply states, ''You know who I am,'' has only posted four messages to date, including one to his cousin.

The heartthrob received a warm welcome for his some of his followers, including his 'Chef' director Jon Favreau, who tweeted: ''You wanted him, you got him. Ladies and gentlemen, give a big #FF to @RobertDowneyJr #chef Show him so love!''

Some of Robert's other well-known followers include Israeli supermodel Bar Refaeli, British actor Sir Ian McKellen, Rosario Dawson, Ryan Seacrest, Ellen Degeneres and 'Two Broke Girls' star Kat Dennings.