I think I might have figured out a way to fix this problem, as strange as that sounds (total newbie's first post, and the work around seems odd at least to me). I was having the exact same problem. I'd bought a download through GameTree and after installing twice wasn't able to find the app anywhere, searching in Spotlight only came up with the installer. The third time I tried to install, I changed the installation directory to my desktop instead. For whatever reason, searching for "Sims" in Spotlight after that actually shows the icon to launch the game. I opened the folder up in Finder and just dragged the icon to my Applications folder, and now it works just fine.