Where's Ellen's selfie? Famous people's tweets vanish from Twitter

, Last Updated: 11:59 AM ET

Some of the most popular tweets on Twitter simply disappeared Tuesday.

Tweets that have disappeared from the site include Ellen Degeneres' Oscars tweet that was retweeted more than 3 million times and the late actor Cory Monteith's final tweet.

Twitter is not sure why the tweets were deleted but is investigating the issue.