Mark C. Palmer writing for Attorney at Work:

While the ABA may liken a “passive” review of potential jurors’ social media to “driving by,” it is not always so simple. The distinction comes when the researcher must log in, or take some affirmative identifying step before accessing the information.

The ethics rules on using social media to investigate jurors differ from state to state, so you’ll have to do some homework in your jurisdiction. In some places, the notification email a service like Twitter sends when you follow someone can by itself be an ethics violation.