Lightroom uses a database, SQLite, to store all of its information about a photo, except for the actual/original photo and its previews. If you want to move a photo, you should do it in Lightroom by dragging and dropping the selected photos in the folder section of the left panel.
Against the advice of all the Lightroom gurus, you have moved the photos outside of Lightroom. Now what? In the filmstrip, Lightroom will show the following:
Lightroom: Missing photo indicator in filmstrip
You need to click on the circled areas and point to the photo in the moved folder.
Lightroom: Locate missing photo
- You only need to do this for the first photo that is located in that folder. Lightroom will automatically update the location of all the missing photos that it finds in that folder or sub-folder.