I believe you asked this once already back in October. The answers did not change. Yes, background investigators can and may look at a candidates facebook. I am not sure about text messages. Would it be a automatic DQ? Hard to say, depends on what the department thinks about it. I don't understand facebook, I can't see putting all kinds of pictures and information about myself on the internet. If your that worried about it just delete the account!
You want to succeed? Deserve it. Outwork everybody in sight. Sweat the small stuff. Sweat the big stuff. Whatever it takes, put your heart and soul into everything you do. Success is a Choice.