Here is a question a parent gave me at the end of one of my seminars: What do you do when your child tells you about some risky behaviors that a friend of his/her is now engaging in and you know the friends parents? Is it different when you don't know the child's parents?
I actually get this question a lot, because I think the underlying thought is:"I would want a parent/friend to tell me if my teen was engaging in risky behaviors. First, if your teen is sharing this information with you, you have hit the jackpot. This means that your teen finds you worthy of his/her trust and thinks that you can help in situations they may feel stymied by. Your first and most important allegiance is to your teen and his/her safety. This is something worth protecting, because it means that you may be able to impact not only the safety of your teen but perhaps someone else's teen as well. If for example your teen comes to you with a story about drinking or a party, it is because they felt uncomfortable, and lacked the experience and strategy to deal with it in a way that left them feeling OK. They don't need your judgement they need your help. If you go right into "the lecture": "You are not allowed to ever go to that house again, if I ever find out you have been drinking or taking drugs, you will be grounded, and I don't want you hanging out with those kids again." You can be assured that your teen will NEVER come to you again for help. If you immediately call the parent of the kid(s) who he/she has told you about, you can also be assured that your teen will NEVER come to you again for help.
Here is what you can do. First, commend your teen for coming to you in the first place. "I really am glad you can tell me this stuff, I know you are worried about your friend, the situation, and now we can figure out together what might be a good plan of action." Now comes the strategy session. Do not try to solve this for your teen, work on it as a collaboration. Come up with alternatives and scripts so they are prepared when this situation happens again....and it will, despite your warnings, punishments and threats. Just by the nature of teen's experimental, and thrill seeking drives, situations that are risky will always be present in their lives. You can't protect them from the situations, but you can give them the information and strategy that will help them when they are in the thick of it. If they are worried about a friend, then help them figure out how they might be able to help that friend before you get on the phone and call the parent.
Your job is to keep your lines of communication open with your teen. If the situation is life-threatening, or threatening to others then this does require a call either to the parent directly or perhaps calling the school's guidance counselor and sharing the information with them. This way, the guidance counselor can call the parents and say that some concerned parents have shared some information I think you ought to know about your teen's safety. Using the school as your go-between allows you to keep your teen out of the loop and protect your trust with him/her while still looking out for the safety of this other child.
If you are friendly with your teen's friend's parent, then you might also use a more indirect approach when having coffee with your friend: " So what do you think our kids are into? Do you think Joey is drinking or fooling around with pot, I just wonder what I would do if I found out?" Now at least you can open up a conversation about your worries, and perhaps get this parent on the same worry page as you, again without divulging any particulars that your teen has shared with you. Your goal for this conversation is to gently nudge this parent into becoming aware of possibilities. You may be sick of me saying this, but your relationship with your teen is THE MOST IMPORTANT goal. Helping him/her to stay safe, may help his/her friends to be safe as well.