Same issue here, clicking on Play in Steam on OSX throws an error “Failed to start game (missing executable)”.
When I open the app directory under ~/Library/Application Support/Steam/SteamApps/common I see two folders there: “res” and “Preorder Special Content” and one file “LICENSE.txt”. There’s no .app or unix executable
Removing the appcache folder and restarting Steam did not help.
Re-installing the game did not help.
Verifying the game files passes with flying colors.