I am pretty sure that multi-select does not help with finding missing photos.
The first thing to do is to check your Folders panel and "relocate" any upper-level missing folders. This should solve 99% of any problems.
After that, individually find any missing photos.
That is what I am trying to do.
I moved the files since I first imported them into lightroom. when i try to "locate" the files it will only locate one file at a time. I am trying to find a way to batch relocate the images. (and yes I have the "find nearby missing photo" option selected!)
In the Library grid view, select one of the photos that is missing (has a "!" on it). Right-click it and do Go To Folder In Library, which will select the containing folder in the Folders panel on the left. If the selected folder has a "?" on it:
that means the entire folder has been moved from where LR thinks it is.
Right-click the folder and do Find Missing Folder.
If it's the parent folder that you moved but the parent is not currently visible in the Folders panel, right-click the folder and do Show Parent Folder. If the parent folder has a "?" on it, then right-click it and do Find Missing Folder.
LR knows the difference between a moved folder and a moved image. You first need to fix the moved folder.