You've been through one of the most painful ordeals any parent will ever experience, and I pray that even in the midst of your grief you'll discover God's peace. I also hope your words will help someone who might be facing a similar situation. The Bible reminds us that "A wise man listens to advice" (Proverbs 12:15).
Yes, drug addiction is a terrible scourge in our society -- and (as you've discovered) simply hoping it will go away doesn't work. Parents need to know the warning signs of drug and alcohol abuse, and confront their son or daughter if they have reason to believe it's taking place. If the problem persists, a pastor or doctor or other trusted advisor can suggest options for treatment.
Parents also need to know who their child's friends are, and how and where they are spending their free time. Teens can be easily influenced by their friends. The Bible warns, "Do not be misled: 'Bad company corrupts good character'" (1 Corinthians 15:33). They always need to know, however, that we love them, which is why we hate to see them heading down the wrong road.
The most important thing any parent can do, however, is to point their children to Jesus Christ -- both by what they say and what they do. The Bible tells us to "set an example... in speech, in life, in love, in faith and in purity" (1 Timothy 4:12).