Would the Titanic pull you down?
Would the Titanic pull you down? However, even with a ship the size of Titanic, the suction created will be so minimal that the only way it would affect you is if you were clinging to her as she sank, allowed her to pull you under for a while, and THEN started swimming for the surface. Cameron's film was accurate on this regard.
Do sharks follow cruise ships?
Somewhere between very few and zero. Cruise ships move far too fast for sharks to follow them. Yes, a shark may have a burst speed that could match a ship, but not one that it could sustain.