An article on the Beeb website wonders whether the current trend of the more informal version of you in French (tu) is going to eclipse the formal vous, at least on Twitter, if not in real life.
Twitter's character limit plays a role here, since it's less characters to use the familiar form, tu, than the more respectful version, vous. The article mentions French magazine editor Laurent Joffrin's question to a follower over Twitter last year: "Who told you it was ok to address me as "tu"?"