I have been looking into this problem for a little while now. Please try some of the advice posted on this post:

http://sketchucation.com/forums/viewtopic.php?f=12%26amp;t=65976

Thanks for your help! I did just as you suggested with success. My custom scrapbook remained too! Again thanks...

I suggested your library folders might be 'hidden' 😒
I keep an alias link to mine in the side bar of the Finder window.
Then you can quickly get into it...
This Materials etc folder has been covered elsewhere on the forum...
http://sketchucation.com/forums/viewtopic.php?f=15&t=52632
On a MAC SketchUp 2013 automatically makes the User's Plugins folder.
However, it doesn't automatically make a User's Materials/Components/Styles folder in the same User location.
You can add those subfolders yourself.
Then you can tell SketchUp to include those in your 'collections' as desired, in the materials-browser's listings etc...