This is an odd one. I have had this happen a few times now. I am working on a project, and I move it or unify or hide other parts, and its gone. I try to find it, most of the time I can, but this time. I would like to know, is there a way to center it on screen? I would like a dubble click or some center object in the subtools. But for now can I be helped? Never mind, I found the frame button.
While you are in edit mode, push F button to frame selection in screen.
Regards
Heiner