Facebook is a social media website used by Blaire and her friends. Laura started sending messages on the anniversary of her death to Blaire and Mitch (the rest are unknown).
When Mitch told Blaire that he was getting messages from Laura Barns' old Facebook account, she told him that he wasn't funny and that you can't joke about things like that. However, she then started getting messages from Laura too. Blaire's response was "who is this".