You've done all you can. The world is vastly different from my own youth. When I was in high school, the main substance abuse issue was chewing gum in class. Today there are all manner of temptations, drugs, alcohol, sex, and all too powerful motor vehicles. This makes being a parent harder than ever.
My own kids went through their own issues and caused me much anguish. I recognized that at some point, I no longer had any control over them, and let them go. Their choices were their own, and some of those were frightening.
Today, my daughter is 22 and my son is 24. Both live on their own, have responsible jobs, don't drink, smoke, or drug. I couldn't be more proud of how they are living their lives.
You've done your best. The title of your initial post, "Please Lord, God... " is a prayer and a cry for God's help. By all means pray often for your son's safety. Don't forget to pray for God to give *you* the support and wisdom you need.