Well you just run into them on a random basis. It's then up to you and/or the other person if you decide to stick together or not for the remainder of the game. If you and the other player drift apart far enough then you won't ever see him/her again. If you had 4 names during the end credits yet you didn't actually see anyone during your time spent playing the game then that's really weird.
My first time I had a long list of names, I saw only one that disappeared when I walked up to him, any other playthroughs had long lists as well but I never saw anyone.