The first step is to locate the mother and child. Once you know where they reside, you can file a petition in their home state for visitation. It may be too late to challenge paternity, because a child support order has been entered.
It is probably too late to request a DNA test. Your opportunity to do so was at the time of the initial proceeding.
You are right that the Office of Child Support Enforcement should have your son's mother's address. You could request that they provide you with that information. If they refuse, I would suggest that you file a complaint for visitation and as part of that action issue a subpoena on the Office of Child Support Enforcement seeking their file. You are definitely going to get an opposition to this tactic.
I suggest that you get an attorney to assist you with this matter.
Please be advised that any information or advice given herein does not constitute an attorney client relationship. Further, before taking any actions or deciding not to take any actions, you should seek counsel of an attorney. This forum cannot provide you with the anyalysis and detail necessary for a full and accurate opinion to be rendered.