Hi, I'd like to help you with your question.
It sounds like your son needs more than just a counselor. If he began struggling with anorexia in his teens like most, then he has had the disorder for a while now. The longer a person goes without treatment, the more difficulty they will have overcoming the problem.
At this point, your son needs more support, starting with his medical condition. If he is not seeing a doctor already, then he should be under the supervision of one. His health needs monitored and the doctor should be determining if your son is digressing and if he may need hospitalization to bring his weight back up.
He also needs nutritional counseling to learn more healthy eating patterns and how to get the best nutritional possible.
He may also want to try medications. There are no medications for anorexia itself, but if your son feels depressed or anxious and it is contributing to his problem, then medications may help lift his mood and calm him.
Support groups may also be another way for your son and you to get support and ideas about how to help himself. Here are some resources for him:
The Anorexia Workbook: How to Accept Yourself, Heal Your Suffering, and Reclaim Your Life by Michelle Heffner, Georg H. Eifert and Steven C. Hayes
Skinny Boy: A Young Man's Battle and Triumph Over Anorexia by Gary A. Grahl
Progress with anorexia can be very slow. And often it can take many years or even a lifetime of battling to deal with anorexia. But with the best treatment possible and some motivation, your son can make a difference in his recovery. Arming himself with resources and places to turn when he feels his anorexia getting the best of him will help him overcome. Your support and efforts also make a big difference. You and your family may also want to consider counseling to help you deal with the stress and come together to find more ways to help your son.
I hope this has helped you,