Does he like nature and animals? Most Aspies do - at least those in my family. Try to suggest going out of town in a quiet place or a park. For starter. We often go to the Aviary here, my young Aspie son and myself (Aspie) love it, I find this place very soothing and love the birds. Less hectic than a zoo full of kids as well.
Is he on medication for his depression?
Maybe you can find a support group for Aspie teens where he could meet kids like him?
I agree with the last post. My son also loves to hike. and run. Photography is also a good outlet. And definitly medication for depression would help
My experience is...once they are 18 its really much harder to deal with. While you are the parent, insist on things, its for his best. Get him involved in things, try to find things he enjoys, animals, the zoo...invite cousins to go or friends he may have, get him into a group that has issues he can relate to. A church youth group is great. Dont allow him to seclude himself, give him time for himself to be alone, but make family time, they want and need schedules I have found this out, find things, pray for help, and have faith, show him affection, give him attention, find things you can commend him for, we all love to be told great job, thats awesome poem you wrote, or you are so smart. Dont give up, tell him he is special, get him involved, he may say noooo....i dont want to, but your the parent, be the parent, make the decisions while you are able to, believe me...once they turn 18 it changes, so these are important years, take advantage of being the boss, God Bless.
I have aspergers and I agree with other posts that your son needs a dog. It doesn't have to be a therapy dog, since he doesn't go to school but a good companion dog. Some aspies like me are very visual non verbal and we don't like noise. Having an art hobby can help him. Maybe you need to make adjustments to your environment so he joins you and the family. Aspies are like animals, very sensitive to noise, movement and sudden changes. You need to get educated and read good aspergers autism books. Temple Grandin has written a lot about the subject.
Sometimes we hear them but we don't listen, so i believe that if you listen to him you'll stop worrying. When he says he's happy and fine then he is. Relax and enjoy him, and love him just as he is.,He seems to enjoy being in his personal environment and i believe when he's ready to change that situation be assured he will. Just be there and he'll be more forthcoming and invite you into his world. I believe they have a lot to teach us, all we have to do is listen. Good luck