Out of Control Teen?

I have a question its about family issues. Ill start off by saying that both the parents are dead though his best freinds mom took custody and that he is 17 years old about to be 18. In Texas he is already an adult. But what do you do with a teenager who is spiriling out of control he was missing for two weeks and we filed a missing persons report and the cops found him high.We can not legaly hold him anywhere like to keep him at home. He's been at freinds place getting high or drunk, But when we go over there to get him they say he is not there. I need advice whats the next step what do we do?

I dont know How to delete this becuse I posted in the wrong spot =/

Intervention?
There's not much you can since he's basically an adult

We did the Intervention the other night. But He told the cops he wasnt sucuidal when he was and he calmed down while they were there so they didnt take him. He has a PTSD, He found both of his parents and now instead of dealing with problems he makes it worse by not dealing. He needs to get help. He keeps talking about sucide, and how he an shoot a cop ect. and its not healthy.

If he's not admitting he has a problem there's nothing you can do
I'm dealing with the same thing with my 16 yr old sister,luckily she's still underaged and now had mandatory out patient therapy every day and has been hospitalized twice in a month
I know it's hard.what have the cops said?
Can you call a local behavior health center and ask for advice?

Cops were the ones who told us about the PTSD and how he was not coping. And weve called and asked different placesbut no one can hold him =/ unwillingly

To be honest, my sister went through that and I was hard into drugs before I had my child and sometimes you gotta let them hit rock bottom before they want help. If they want to be like that theres nothing you can say to change their mind. For me getting pregnant made me stop and havent touched it since but for others like my sister she had to screw up so bad that she finally said wtf am I doing. You can't force someone to stop but if you cut the person off of everything (money, shelter, food) they may see that theyve screwed up. Not saying it will work but that's all I can say, hope it helps in some way.