I’m forever seeing appeals for missing people on local Facebook groups. I’m always a bit suspicious when the OP says police are searching for the person, but if you know anything message the OP directly. Surely if police are searching, it would be better to inform the police, get the information firsthand to them? Facebook randoms don’t know why this person has left their home, they may have left for a very good reason, they may be fleeing domestic abuse for all we know.
AIBU to ask you, if you do see one of these posts, and you do have an idea of where one of these people is, to tell the police directly? Surely the aim of these posts is to find the missing person, and the police are the best placed to do that and protect the missing person if they need it?