Why has has my friend's Facebook account changed its name to John Smith and tells me i am not his friend?

[Metal Man]

SO recently my Friend, lets call him Andrew Harvey vanished off facebook, naturally firstly I thought he might have deleted his account and someone told me he had, but then, when I went to look at a page I created with 5 members (private page - to be a member they have to be added by me personally) then I noticed, all Andrews posts were still there, under a name of "John Smith" I am certain this is my friends account because I looked at my message inbox and the messages that had come from him are now said to be from a "John Smith". I searched the Internet, thought he might have deactivated it, but the name is still hyperlinked which apparently means it isnt deactivated. all I can see on my friends page is this: https://www.facebook.com/John.Smith.69q under the nonexistent profile photo is "if you know John send him a message" all his posts, pictures, about info and videos are unaccessible to me (all my other friends say they cant see them either) any idea whats happened ?? he's no longer on my friend list and I can't send a friend request to him either. he hasn't replied to my or anyone elses texts or phonecalls so I cant ask him. we dont know whats happened to him, please HELP!!!!!
I cant call him or text him, do you have any proof he's been hacked?