For puppies to bite playfully is normal, but when it's getting out of hand, you need to discipline him. I'm guessing that your pup wasn't with his littermates and mom long enough to learn the fine line between soft chewing and painful biting. They were supposed to bite back or yelp to let your puppy know, "Hey! Enough is enough!"
Yeah, using a toy to refocus his attention to biting the toy instead of your hand is good, BUT IT'S TEMPORARY. I highly suggest mimicking what mama and siblings would do in this case. I learned this from a few people and Cesar Millan. Use your hand as a "mouth" and give him a quick nip in the neck ONCE. (It shouldn't hurt him, this should be more like a surprise shock). While you do this, you should make a sharp "Eh!" I'm sorry if this all sounds pretty vague, lol. Good luck, and remember that YOU'RE the boss.
