The thumbnails of 3D warehouse models are not showing. Trying directly from the SU.
Sketchup 2017. When I put this link < 3D Warehouse > in the search bar, it returns this
Im having the same issue. Thumbnails are not showing up. Sketchup 2017 . Mac OS 10.12.6
Interesting. Thumbnails are working here. There was some work done on the Warehouse in the last day or so. You might try clearing caches and see if that helps.
Did not work 
Can you see the thumbnails if you open the Warehouse in your browser?
They have said they are working on the Warehouse so perhaps you just need to be patient.
Please complete your profile with SU version and license type.
This seems to affect 2017 versions.(Make and Pro) Try if deleting the Webcache folder works:
C:\Users\ USERNAME \AppData\Roaming\SketchUp\SketchUp 2017\Webcache
Thanks for reporting this. It looks like we have an issue on older versions of Chrome (which is what we use in SketchUp 2017). We are working on a fix now and should have something out by later today. In the meantime you can still use 3DWarehouse in your regular system browser (the latest versions of Chrome, Firefox, or Safari).
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Oh, right! Thanks for your attention!