If family are around, agree that they should come first.
I thought about contacting the school when I was worried about my friend, but just couldn't do it in the end. It seemed such a betrayal. However if no family can help and you are really at your wits end, it might be a possibility. I was advised to do this by local social services.
When I phoned the local social services department in my friend's case and they told me I could talk to them anonymously about my friend and they would follow it up. But in the end,I just couldn't do it, so kept in close contact with my friend on the phone, and also phoned her sister (who was more aware than me of the problems). She drove down to see her and things got sorted from there. It was lucky there was family prepared to help and not stand by.