My bestfriend has a drug problem and I don't know what to do.

My best friend (who is 15 years old) has been doing cocaine for the last few months and it is getting pretty clear to me that she has a problem. She doesn't go to school and has been binging every single night til 5 in the morning. The only time she doesn't binge is when she doesn't have the energy to do so.

I've had past cocaine problems myself so I've had to distance myself from her to prevent myself from doing it.

I've been talking to her sister about this whole problem and it seems her sister lost hope in her a long time ago and wants nothing to do with the situation.

I even tried telling her mother via a facebook inbox. I know her mom knows she is doing it but she seems to be in shock at the moment and not doing anything to help. I know her mom got my message but she isn't responding.

I've been able to get her to admit she has a problem but at the same time she doesn't seem to care what direction her life is going in. I'm her only true friend and i try to tell her what's going to happen i try everything.

She has made the decision to stop a few times but as soon as i lose contact with her she'll get a text from one of her coke buddies and go do it anyway.

What should i do? I'm only 19 years old and the only person in her life that cares enough to go to these lengths to help her. My last resort is contacting her father about the issue but I'm not sure what will happen if i do.