What if they don’t want to be found?

I see those posts on local FB pages too, and always want to post a warning about giving information without the person's permission. But I haven't been brave enough, yet. I probably should though.

This was mentioned on my last safeguarding training day. Case study was a child in foster care, had been removed from their birth family due to abuse. The birth family posted photos of her on these types of social media groups and were eventually able to track her down. The issues discussed in that segment were around information sharing, even when well-intentioned, and being mindful of wider implications.

I don't know whether is a still thing because I never buy The Big Issue these days but back in the 1990s it used to run an item every week whereby 4 people were featured. People that had gone missing or walked out on their lives,sometimes years and years ago. It gave brief detail about the person and would say who it was that was worried about them . And it always made it clear that if the missing person got in touch they would never pass their current whereabouts or details on to anybody unless the missing person wanted this to happen. All they would do would be tell the person or people who were concerned for their welfare that they were alive and alright.
I thought this was a really sensitive and decent approach. Because OP ,as you say ,nobody knows why people lose contact with other people and very many probably don't want anything to do with their old lives or friends or family

I worked with the Missing People charity a few years ago, on their helpline and a surprising number of calls were from people who had seen the MP posters about them and didn't want to be "found". The police also quite often refused the charity permission to highlight a particular person's disappearance (all publicity has to approved by the police), as they had inside knowledge around why the person might have left.
Having said that though it still left families heartbroken, as although the reasons for not reconnecting might be clear to the missing individual, they weren't always to the family.

I agree and in most circumstances I see it's from well meaning younger people who don't understand the deeper meanings as to why families lose touch etc.... or they don't see why they shouldn't naively tag auntie mavis .......or it's from the much older generation on Facebook who are loving the memories and have no idea of the etiquette on Facebook. It's the same generation that see a dog lost in "shelves way" nowhere town,London.... and then put it on their wall and reply "shared Manchester x".

(I'm 50 plus by the way so fall I neither category!!).

There is a lady on my local FB pages who repeatedly, unbelievably repeatedly is looking for her adopted daughter. It's a very sad story, on her part, I get it. But equally she can't see the other side of the coin that both her DD might not want to be found and we don't know her DD from the vague details... we can't help her either.

I agree, I've seen a few posts like this and I'd never give out someone's location, contact details etc - like you say you don't know why they lost contact. Worse case scenario is they could've tried to escape abuse and start afresh. If I recognised someone in a post like this I'd always go to them and say please be aware so-and-so is trying to find you.

Yes, YANBU. As you say, you never know why someone got out of touch.