I have never used linkedin. Don't plan to. There are various online job websites where employers list job openings.
Facebook, I keep mine semi-anonymous. Closed to just friends. I reject friend invites to friend of a friend or someone I hardly knew anyway. No pictures. Rarely comment. I may say the occasional happy birthday to someone I friended, get well soon, or LOL or "like" a post by a friend. It's kind of introverted but I keep my profile on the down-low.
Think about this, Derek Jeter is an all-star, high profile mofo with tons of cash and has had super-hot girlfriends... but he's very incognito, as in the paparazzi don't have any sneaky photos of him. TMZ has nothing on him. You need to be like Jeter. Stay out of trouble, don't look for trouble, and don't walk into a situation that would look bad if the media caught you. He probably doesn't bother with hooking up with a one-nighter or side-piece, which is a good thing. He can't be exposed, blackmailed, or has anything that can be used by an angry girlfriend or jump-off against him. No DNA/paternity suits. Clean and worry free.