Have you ever called or visited someone who's gone missing, just to see if they're all right?

Yes, often. I have a pretty predictable group of friends, if someone is out of touch without notice I try to contact them.

Yes, people in 12 Step groups will check on people that disappear.

There was a homeless man that sold Street Sheet at the Whole Fooods in Berkeley that my old girlfriend and I got to know. We even got to know his daughter. Michael did well at times, and struggled sometimes. The last time he disappeared for a couple months, we checked with his daughter and learned he had died.

Yes to all 4 of the OP’s questions. For example, I know someone who’s battling lung cancer and I’ll send him an email to check in on him if I haven’t seen him for a while.

I haven’t visited, but I’ve made a point to ask someone who knows the person well if the person I’m concerned about is out of town or ok. So far, the few times I have asked, the person I asked knew the answer, and I didn’t have to consider further action. I live in a 55 and up community, so we worry when someone stops showing up. Some people are snowbirds or snowflakes (only live here part time) but also, unfortunately, we have more illness and death than a standard all ages community.

Thanks for bringing this up. Starting today I will !
If I don’t see someone for a while I figure they are just busy. I never give it a thought. I have friends I don;t see for months. When we do finally get together we catch up in minutes. We don’t check up on each other regularly. Maybe we should.

I will admit to sending a pm or two to people here whom I’ve not see or spoken to in a while.

It’s a troublesome business acquiring a reputation for fixing things. Believe me, if you allow it to happen, you will never have a moment’s peace.

I knocked on their door but they were missing so unsurprisingly weren’t at home.