I have exactly the same problem as you. "Panels" is all that exists, and "Required" is nowhere to be found.
/Applications/Adobe\ Photoshop\ CS6/Plug-ins/Panels is my file path.
The instruction for my plugin says:
Using the Finder, move the file ToneMapping.plugin to the Filters folder of your Photoshop Plug-Ins directory:
If you have Photoshop CS6, move the file ToneMapping.plugin to Applications/Adobe Photoshop CS6/Plug-Ins/Filters
Which doesn't exist.
I've deleted all the misguided "answers" previously provided.
The location of a third party plugin inside the plugins folder doesn't matter.
Just put it anywhere inside the Plug-Ins folder.
The Filters/FileFormats/Extensions/etc. subfolders were just for user convenience - Photoshop doesn't really care about the location as long as a plugin is inside the plugins folder.
For a variety of reasons, we moved the default Adobe plugins into the Required folder (kind of hidden inside the app package on MacOS, but visible on Windows).
The top level Plug-Ins folder is now just for your third party plugins.
I recommend, if you're copying your own plug-ins from whatever sources into your plug-ins folder (vs. using an installer), that you create subfolders that are plainly named. That way you'll know what they are at some time in the future instead of trying to figure it out from some short, cryptic name.
As an example, from my own system:
Directory of C:\Program Files (x86)\Adobe\Adobe Photoshop CS6\Plug-ins
09/21/2012 10:22 PM <DIR> .
09/21/2012 10:22 PM <DIR> ..
04/05/2012 05:52 PM <DIR> Astra Image
04/14/2012 09:11 PM <DIR> FITS Liberator
04/14/2012 11:04 PM <DIR> Focus Magic
09/21/2012 05:03 PM <DIR> Hasta La Vista Green
04/14/2012 10:44 PM <DIR> Kodak Photo CD from PS 6
09/21/2012 10:22 PM <DIR> Optional Adobe Plug-ins
05/07/2012 06:43 AM <DIR> Panels
04/05/2012 05:52 PM <DIR> Perfect Resize 7.0.plugin