When Should I Be Worried About My Son?

Goth isn't a cry for help, there could be MUCH, much worse problems then that! He is just trying to find his identity.  Tell him you trust his judgment and he is important to you. Let him know if he does need help with anything, you will be there for him.  
He might roll his eyes at you, but at least he will think about it and know that you love him!  =)

Stand by your child,you can voice your opinion on some things but allow him to become himself,at 13 you still have say,are you spending a lot of time with him doing things that you like to do and sharing that information with him talk about what it was like when you were growing up,what you and his grand dad use to do together fish,toss a few balls etc just man to man talks.....hope this helps