You may have done this already, but did you "un-zip" the ToolsOnSurface_131.zip file? If you didn't and just dropped the .zip file in the plugins folder, it won't work. If you don't have the software to decompress the archive ("unzip the .zip"), you can find free software to do it.
7zip is free: http://www.7-zip.org/ and will do the job.
Here's what should be available in Sketchup:
Tools on surface in the "tools" drop down menu: