Will a child that is socially behind catch up on their own or do they require special intervention? He is now at least two years behind socially.

No. It depends on why he is socially behind but in general a child who is 2 years socially behind has some subttle but significant impairment interfering with his ability to learn social skills. Seek out an evaluation by a developmental & behavioral pediatrician or a psychologist who does such evaluations. Other parents or your pediatrician are often the best sources for a referral in your area.
Needs intervention! Early intervention is really important. You should fill out the modified checklist for autism in toddlers and take it to your doctor. Https://www. Firstsigns. Org/downloads/m-chat. Pdf. Your doctor should also use a formal developmental screening tool like the asq3 or peds21.