I've been through some depression (ok, a lot), and I've posted very negative status updates on my facebook before, including some updates that were suicidal in nature, when I was suicidal. It's easy to just click a link, leave a page and forget about what you read about a friend. I'm not saying call the cops or whatever, but I think it is certainly important to take action when you read something very negative online. It's amazing what a phone call, or a simple message on facebook can do. It really can save a life. Just ask what they are up to, or strike up a worthless conversation, then slowly try to figure out what is wrong. That's what people have done for me, and I've also done it for other people, and it really helps.