How do i connect CS:GO to Gmod?

I have searched around, and I have been unable to get a definitive answer as to how to connect CS:GO to Gmod. Is there some compatibility issue with CS:GO being too new? I just want to know what I am doing wrong, and why I cannot get it to connect. When I check the list of games I can connect, the only one is TF2. CS:GO shows up, but it wont connect.

Please help.

BTW, I am currently using gmod 13 (most recent update, including today’s update).

Also, I know this is probably a stupid question, but I can’t find the real reason for it.