I would probably put a few pennies in a small metal container to carry around and shake it (not too hard) if he growls.
I do believe he needs to be socialized much more and quickly before he gets much older. Take him around many of your friends and family. Allow him to experience different situations and other small dogs and set up some play dates so that he can socialize with them as well.
Socialize your little dogs as early and as much as possible and you will have a pet that other people enjoy.
