Be careful with neck bridge advice, can be dangerous on neck. Plus there were dozens of guys in wrestling doing them without much too show, so I don't think it builds the neck much. Best answer is if u have access to a Hammer strength 4 way neck machine, use it 2 times a week (in addition to heavy shrugs) 2 sets each direction. I did this 2-3 years in college (we had 2 of the machines) and my neck size and strength surpassed 10 years of bridging exercises, and got pretty thick and more importantly--strong.
If no machine, buy a $10 neck harness at any sporting good store, and use for back. For front and sides, fold a towel and put a plate on forehead and temples and do "sit ups" for your neck off end of a bench. Good luck!