If items hidden in a stack meet the search criteria, they will be found. This is different from Aperture (if that's confusing you) where you need to include stacks in smart albums.
I have Lightroom CC and this is not the case. I have a folder with some stacked images including some images which are" .TIF" files. If the ".TIF" file is at the top of the stack, then a search for TIF files will show it. If the stack is un-stacked, the search will find the TIF file. If the ".TIF" file is in a stack but not the top image, a search for TIF files will not find it. Of course I can un-stack the whole folder. But then I need to re-stack each image sequence afterwards. Not very satisfactory! Incidently I have searched by using "Metedata", "FIle Type" and also "Filename contains .TIF". Neither work if the images I am looking for is stacked.
OK, I see what you mean. Just select all, hit S and the stacks expand. It's the same operation to close the stacks.
There's also a menu command to expand all stacks.
Thanks John. That's the answer. I was not aware that it automatically re-stack images after un-stacking them.