I’m a newbie to SketchUp. I’ve completed my designs, and downloaded the Vray demo for rendering, but I can’t ‘find’ it. How do I get Vray to work as an extension? SketchUp doesn’t recognise that I’ve downloaded it, as far as I can tell.
Did you check this help manual for Vray setup and installation?
Vray version is not stated, but considering the current beta version (v3) does not have demo. Therefore I suppose OP is trying to use v2.0 demo with SketchUp 2017. And as @sketch3d_de has stated, V-Ray 3 beta is the only version working with SketchUp 2017. Perhaps revert back to SketchUp 2016 for the time you are using the demo.