That's what puppies do; It's the teething stage. Be sure he has plenty of things to chew on such as toys, bully sticks, etc. I've found the Hide-A-Squirrel to be a good entertainer. It's a toy where they have to pull squirrels out of the hive. They're available at PetSmart. Somebody also mentioned bitter apple spray which works well to keep their little mouth off of things you don't want chewed.
Good luck!!
And if you want to try a Bully Stick, just let me know. (PM is best) I will send you a free sample.