[zolthrowaway]

Please don't do that. Very often depressed people are incredibly aware that they aren't being social and they're stuck in a rut. Just be a friend. Just based off wanting to help, you already seem like a good one. Check in on them from time to time. Just a simple text occasionally can mean a lot. Ask them how they are. Be prepared to not get non-answers. Be prepared to be walled out sometimes. If they ever want to talk, be there to listen. That will help a ton. Just be there for them.

Depression is a real bitch. It manifests itself differently in everyone. Perhaps coaxing someone to see a therapist, go out or whatever would actually help them. But that's not going to be true for everyone and the coaxing may do more damage than good if it's unprompted. If they express interest in anything (e:g; going to a movie, seeing a therapist, going to the gym), that can be a good time to give them a small nudge. I hope your friends find some light in their tunnels.