I currently have 15 trackables belonging to other cachers in my inventory. However, this is because I am going to Northern Norway into the Arctic Circle in just over a week and I have contacted every single owner and asked if they want to go. I also find a traveller in an average of 1 in 20 caches but most do seem to be at events. I am also releasing 8 of my own TBs when I am in Norway for them to travel. I have also just put 3 new TBs into an event for when I get back. These will moved into a new series of caches as soon as they are published for that event.
I have seven travelers currently traveling around the world and have had none go permanently missing. From reading the other posts I guess I am just lucky!