I'm not big on posting here.....or giving advice/info willy-nilly. That said, a few issues come to mind that may help BOLSTER YOUR CONFIDENCE & COURAGE.
FALSE IMPRISONMENT......is exactly what's happening. No court order, means voluntary intake. As much as I remember, the management of this "facility" are liable for criminal and civil penalties. Contact a PATROL SARGEANT of the local law enforcement to escort you on the property to "maintain order" and have your son returned.
LARCENY....the UNLAWFUL KEEPING OF ONE'S PROPERTY. Just mentioning this and false imprisonment in a businesslike manner will get the point across. Example: I went to a car dealer for a "trade-in", they tried the "strong-arm" tactic of not returning my keys. It was amazing how quickly the keys were returned when I told them they're running the risk of grand larceny.
LOSS OF WEIGHT.....If he's on a stimulant for ADD, it could hamper his dietary intake. HOWEVER, one thought came to mind, it might be anorexia. Many teens suffer this disorder because their body is the only thing of which they have "control". (I had anexoria from 17-19 years, weighing 89 poinds at 5'5", due to a tulmltous home life with a pain-med addicted father and bi-polar mother).
Keep him with you, Mama Bear, and find a mental health professional to assist with counseling Lots of "quacks" out there, go with your gut feeling (you're his mama). Perhaps a proper diagnosis and plan to help him get through this traumatic ordeal would be in order. (Our son has Aspergers Syndrome and engaged in many "go rounds" with "professionals".....took us 5 years to find a common sense doctor.)
My prayers are with you.
Cindy