Popular multiplayer games on Steam for 15 dollars or less?

I'd say take a look at killing floor when the sale happens. It's got a pretty good playerbase and is fun. The sequel just came out so it should be on a pretty good sale

PAYDAY 2 is a great co-op game! Usually gets down to 6-7$ every time there's a sales season on Steam. I'd say you give it a try ;)

don't starve together... Don't Starve Together

HAWKEN. Free to play, (not pay to win), there are usually players playing, but not that much at the moment, (averaging at few hundred). Playerbase steadily rising, however. Gameplay: unique.

Ask again later.

Counter Stricke: Global Offencive $9.99

http://store.steampowered.com/stats/

TF2 = 0$

The summer sale is about to start. Wait just a few more days. :)

Can people please look at my games before posting? I have almost all the games you posted...

Magic 2015.
Got about 400-500 people on usually, which should be enough for multiplayer.
Goes for under $5 during sale.

csgo, chivalry

Awesomenauts - much fun (But I see you already have it.. so never mind :P)