The official Richard Castle Twitter Account.
First tweet was made on 27th July 2009 and said:
Hey this is Alexis – just set this account up for my dad – he’s a little unsure about it. Tweet him so he feels welcome!
During the break between seasons 1 and 2 Richard Castle tweeted about his vacation in the Hamptons where he solved a murder mystery via twitter. He did the same during the break between seasons 2 and 3.