Did you try the "common" folder?
it was in my username folder. thats why it did not install steam pipe for the game.while it was there steam said "failed to start game. missing executable"
it shouldn't take long. when i logged in it installed in 5 minutes :I
people ignore this post please. it is completely false. My gmod did not have steam pipe.
off topic: why is portal 2 starting up and then ctd's (crash to desktop with no error)