Rumors among friends, to tell or not.

We have been family friends with our neighbors who I will call the smiths (not their real names) for more than 20 years. They are lovely people. Our daughters were born one year apart and were best friends for a lot of years in early childhood. Once they got into middle school and high school the grade difference got big and they drifted apart and now very rarely socialize anymore. I think they also turned into slightly different people along the way. Well then, my daughter came home from a high school party last night and told me a very disturbing story about her old friend. Apparently, the girl (who is now 16) was drunk at the party and was exchanging sexual favors for alcohol and drugs. I asked my daughter if she was sure it was true and she said that she was. She said the girl was pretty wild and drank a lot but she had never seen her do anything like this before. She said she overheard the girl ‘make a deal’ with a group of boys before going into a bedroom with them. I am shocked and saddened by this. I remember her as this sweet little red headed girl at my kitchen table. But now I don’t know what to do. Should I tell her parents what I learned? How could I tell them in a way that wouldn’t hurt them irreparably? I also worry about being ‘the messenger’ for such tidings. This may seem selfish, but I do not want to damage our friendly relationship either. Should I tell our pastor and ask him to speak with them? I do not want to spread this any further around than need be, of course.