You can call the parent who is hosting the party if it is in a home. Your child will be embarrassed by this, perhaps, but it may be worth it to get to the truth. But, the thing is that it's likely that somewhere, somehow, your teen is going to be a party where there is alcohol. The best strategy is to talk to your child about drinking way before this happens. Open and honest communication needs to begin early between you and your child and it needs to be consistent. Explain the perils of underage drinking and of drinking to excess. Strive to make sure your child doesn't see you drunk or it will be much harder for him to understand why you think it's so bad. Make sure your child knows that you are against him/her drinking underage or drinking to excess and that it is not okay with you. While some parents choose to look the other way, believing that all teens will experiment with alcohol, the kids who know that their parents care and take this seriously are far less likely to indulge. Build your child's self esteem beginning at birth so that he/she is strong enough to withstand the peer pressure. Talk about peer pressure and the strategies your kid can use to stand up to them. This is not a one-day fix. This lesson takes much of your child's life to learn. Go online and gather some statistics about kids who have actually died on prom night and share those stories with your child too. Then, hope for the best. If you trust your child (and tell him her if you do), that will make all the difference.