Do you have an exclamation mark on the images?
If yes then please follow the below article to link the images again in Lightroom
If you do not have the images in Lightroom at all, then you may re-import them in Lightroom suing the import function.
May I also know one thing when you hit the synchronize folder option, do you get a dialog box showing you the missing images?
No exclamation mark. There is a folder in "Catalog" called missing photographs. I need to move the pictures from missing photograph's into my folder.
I'm really not sure what happened when I hit synchronize. I accidentally deleted so when I re added I added my back up folder. But now every time I try to synchronize back up folder it says my pictures are offline or missing.
Please follow the steps mentioned in the above mentioned thread to re-link the images.