I just found this thread because I placed my first geocoin and it has also gone missing. I think it's pretty obvious that they are meant to travel. I was very new to geocaching the first time I ever found one and at first I was excited at finding such a cool trinket -- but then VERY quickly realized that it read right on it that it was a trackable coin. All it said was "Track this coin at geocaching.com" and that was all I needed to read. Geocachers should educate themselves on the etiquette of geocaching before they head out. The one I left had a tag on it that read "DONT KEEP - TRACK @GEOCACHING.COM / WANTS TO TRAVEL WORLD & END UP IN SCOTLAND" and I figured once it's there if anyone who finds it there and wants to keep it, they can. I knew there was a good chance it could be muggled, but it was the only thing missing from the cache, so it was likely a geocacher. Hopefully they will figure it out and get it moving again. Some of your posts have given me hope.
And to the people who say they thought they could keep any geocoins they've found, you are incorrect. If you still have them PLEASE log them online and see what the intention of the coin was -- most likely the person who left it wants to see how far it can travel, and you screwed it up Thank you for getting it/them moving again; you'll make someone's day!! And pass the word along to any other ignorant geocachers.