Hello Janjan,
Welcome to the forums. Whilst I can't offer you any advice based on how to deal with your son I can offer you advice that may echo your sons perspective. I've just turned 23, about 6 months my parents both finally decided to stop supporting me and gave me one weeks notice to leave the house. At this time I was losing my job and going bankrupt as well.
So I left, and it made me want to go to rehab, so I did. Now obviously I don't know what level your son is at in his addiction or what he is thinking about anything. I know that my parents 'letting go of me' gave me that final oomph I needed to reach my rock bottom. I bet somewhere in his mind is a willingness to sort himself out. The only thing you can do is not help him and let it happen when he is ready to sort it out himself. Obviously if you have any concerns about his mental wellbeing you should contact the relevant authorities.
Natom.