Have you checked out his friends especially at school maybe invite them round to the house , you say this is new behavior has he recently started a new school or activity?
That is such a vulnerable age! So much going on---- bodies changing, stress increasing due to more demands academically and socially, more opportunity to get into things that can cause serious issues.
Have you been able to sit down and talk with him that you are concerned and are noticing these changes? Ask him what he thinks is going on. I would make sure to do it in such a way that he doesn't become defensive but rather that you care about him and want him to be happy and to feel good.
I hope it isn't drugs. That seems to start younger and younger these days. Talk to him first to see what he can explain is going on. He may say nothing but open up if you continue to show you are empathetic to him. good luck
I believe there is a drug test parents can try now if they suspect their kids may be on drugs .Could there be any school bullying going on , what happens prior to an angry out burst,what is he angry about ? And yes I am sure some changes at puberty may also be contributing .