Thank you for the request.
Any SSRI will be effective. Paxil, Prozac, Celexa are all examples of commonly used SSRIs. The thing to know with SSRIs or any medication is that each person reacts differently. Everyone has different body chemistry so a medication that works for one person may not work for another. It is very common for people who take medications to try different ones until they find one that is compatible with their own body chemistry.
Here is a good guide to medications for your son:
It sounds like your son needs a thorough evaluation. The symptoms you are describing, including the lack of social skills and acting and dressing like a 15 or 16 year old, sound more like someone with Asperger's disorder or a Pervasive Developmental Disorder rather than someone with OCD. OCD is an anxiety disorder, which does not affect a person's development levels or social skills to that extent.
Here is a listing for therapists available in your area that specialize in OCD. If they cannot help you get an evaluation for your son, they will be able to refer you if need be. Most therapists are trained to evaluate and diagnose, but if you feel your son needs more specific treatment or more intensive, such as hospitalization, then the therapists will be able to refer you. They will be the most knowledgeable of the resources in your area for people with OCD.
You also may want to contact NAMI for other resources in your area. The will know the best options for your son and for support for you and your family.
The best option though still would be getting your son a full evaluation. He does not seem to be diagnosed appropriately. Having the right diagnosis will help you find the correct treatment for your son so he can recover and lead a normal life.