Here are the instructions for fixing the problem
http://www.computer-darkroom.com/lr2_find_folder/find-folder-old.htm
Your problem probably happened because you moved the photos (or the folders that contain them) outside of Lightroom. So don't do that any more. Develop a workflow that doesn't require moving photos from here to there; better yet organize via keywords and other metadata and use default folder names such as capture date.