How do you do it if you go missing?
I find it fascinating, especially the go out for a pint of milk and never come back thing.
So, you leave, leave your job, but how do you set up in a new town without anyone knowing? Even assuming money is no issue, you just rock up to a new town, stay in a hotel and rent a new flat, then apply for a new job? Get a new phone and just make all new friends?
Yes it is basically this.
It would obviously be easy for the police to find you if you've used a card from a bank account in your name, got a flat to yourself so there's no escaping being on the electoral roll, or got a legitimate job involving giving them your national insurance number to be paid. If you're an adult though, the police can't tell your family where you are if you don't want them to.
It's not so difficult to not have social media. Easy enough to save up cash if you don't want to be traced through your bank account. If you live somewhere your "landlord" is illegally subletting the property or you're renting a room in a house-share, it's easy enough to not be on any official records there. Some industries it's still possible to get cash-in-hand jobs and this used to be even easier in the past, so no employee/tax records. PAYG phones and their SIMs don't need to be registered, you can pay the monthly fee with a voucher that you can purchase for cash in most convenience stores and supermarkets, and you're good to go. Making new friends is easy if you're the chatty sort and not too picky who your friends are or the kind of person who has lots of acquaintances you hang out with but no real friends, not everyone is going to pry into your background and history.
Even getting a legitimate job and flat is easy to do without family or friends knowing, you can apply for jobs and go through the entire hiriy process without telling anyone, rent flats without a guarantor if you've sufficient income, perhaps taking a day trip somewhere to do so and not telling anyone about it.
I've never disappeared in this way but I have moved around a lot and distancing yourself from someone you'd rather not be in contact with any more is as easy as not telling them or those who knows them what you're doing or where you're going, then changing your phone number and not giving it to them. If they only contact you sporadically anyway it'll be ages before they realise your phone number no longer belongs to you. If they're on your social media you can block them easily. In my case I'm generally taking the opportunity of a move to get rid of anyone who drags me down with negativity or who I find to be a toxic personality, rather than moving specifically to get away from them, but the end result is the same.
It depends on the sort of life you lead really. My family don't know who my friends are and vice versa, it's not a secret it's just why would they? I'm not close with family, even when I was young and lived with them. My friends come from wherever we've met and often don't know each other, I'm not the kind to host massive meet-ups of everyone I know. If perhaps you live in a small town and everyone in your life overlaps, then you're maybe looking at having to go no-contact with them all to achieve it with one of them.