The moment I saw the title of this thread, my first thought was Andrew Gosden, and then he was mentioned in the very first post. I haven't read all the pages of this thread yet so apologies if I'm repeating things others have said, but his case has always stuck with me. Andrew Gosden is a similar age to me, and when I saw his case on the news as a teenager I couldn't help but think that he reminded me of myself, and he seemed like the sort of person I could've been friends with at school. I think that's why this case has made such a lasting impression on me.
The things that gets me is that he seemed to have left at least somewhat of his own accord. He seemed to have planned to go to London, and bought the ticket and travelled there by himself. Was his reason for going to London the same reason he disappeared? Or was he planning on coming home and then something else happened to him that he didn't expect? It's frustrating that the CCTV in London wasn't checked until most of it had been deleted, otherwise we could've known where he went from King's Cross. There's part of me that hopes that he'll just turn up alive and well one day, and he will have started a new life for whatever reason. But I know there are people who disagree with that and think something bad must have happened to him. I just hope that there's some kind of closure on this case at some point.