Ask HN: How to help someone going through depression?

I have a friend who lives about an hour from me and I recently found out that he had secluded himself in his room for a few months. My friends and I have been trying to invite him to go out but he doesn't want to. All my friends are saying, "He doesn't want to hang out, just let him be", but I'm worried about his mental health. Today I invited him to my birthday dinner (6 people total, all of whom he knows) and he refused. His parents have given up on him, which is really sad for me to see. Is there more I can do to help?