Me and my buddy are completely lost. We just killed the guy with the virus. Our goal is to kill the rest of the guys on the platform. We've searched everywhere on the map. There isn't anyone left standing as far as I can tell.  Has anyone completed this level?

I was completely lost in every level of that game's co-op play.

Was it the level with the empty railway station? Where you have to follow someone? I think after killing the guy, there should be a vent, and then you just have to shoot some glass you stand on, and fall on a train to complete the mission. Anyway there are walkthroughs on the net. See youtube or gamefaqs.

I beat the co op a long ass time ago so I don't remember anything. sorry I'm no help man. check youtube.