Just subscribe to the mod and it'll automatically download. I play L4D2 on Mac as well and I haven't encountered any issues.

Ive subscribed and they have downloaded but i open my game and they arent there

You will have to wait for them to load. So you open up the game, wait a while and then open up your add-ons.

same thing happened to me on my mac osx mavericks and i can only use certain mods

i subscribed last night. how do i check to download them?

i think you go on the game and and go to add ons and they will download, but some mods arnt for mac sadly, i am trying to figure out how to check if its for mac before i download it 8==>

thanks to all! Figured it out!

howwwww

I did what WingMaven said and closed my game after downloading, waited a few hours and opened it back up and it worked. I also restarted Steam.

k, thnks