Firstly I’d like to wish you and your family much hatzlacha with this. My heart goes out to all of you.
A few things:
1. Try to give as much warmth and love to your son as he goes through this. Try to instill an environment where he knows that he can be open with you, no matter how difficult the situation is.
There are many reasons why a frum victim might not name their abuser. Examples are (but not limited to) not wanting to get them into trouble, fear of revenge, fear of the backlash when he names the person, fear of speaking lashon hara, protecting the family.
Try to show your son that none of these are reasons to be quiet.
2. Get yourself some help. People often think that the child is the only victim. The parents also become victims. I can tell from your SN and your posts that this is unimaginably difficult for you. In the same way that you want to get your son assistance, get some for yourself.
Good Luck