Ask them directly if they have a plan. Be very wary if they are giving away precious possessions. If they are at either of these points go seek out an adult. It takes a lot of courage to do this but it also proves what a good friend you are.
It depends on their relationship with their parents. Of course telling their parents would be ideal, but it could make the situation a lot worse. At times like this, trust is very fragile and it should not be broken under any circumstance. You should keep it between you and your friend because they need somebody to talk to without being betrayed and their parents who may not understand making it worse/pressuring to instantly get better. When I was in middle school, there was a girl who self harmed, was anorexic and was really depressed (I didnt know her personally, but I saw...). At the end of the year, she made a friend. She told him- he told her parents. Her parents made it worse. They pressured her to instantly get better. She couldn't take it-- she killed herself because her parents never treated her the same, they would never drop the topic of mental health. This girl only got more problems. It depends on the situation and what your friend says about telling somebody.