The latest article on jurors and social media is listed below. Among
other things, the article lists four reasons why courts are so concerned
about jurors using social media.
(1) Potential for direct communication with members of the court
(2) Release of confidential information about the trial or the deliberation process
(3) Disclosing of personal information about a fellow juror
(4) Revealing an unacceptable bias for or against one party
I would add one more reason to this list or maybe expand #1.
Potential for communication with outside parties unaffiliated with the court.
When jurors use social media they are likely to post or write about the case. This increases the likelihood that they will get into a discussion or communication with an outside party about the case. This in turn may lead to the outside party improperly influencing the juror.
Social Media Use as Evidence of Juror Misconduct: Richard Raysman and Peter Brown
I have written two law review articles on this topic.