L4D & L4D2 (PCGamingWiki articles) support: 2-player local split-screen co-op - Survivors vs AI. 4-player online (multiplayer, but cooperative) - Survivors vs AI. 8-player online (multiplayer, but cooperative and split teams) - Survivors vs Infected. There are also modded servers, at least for L4D2; I don't own L4D so of course haven't tested it.
To do that, you go to \SteamApps\common\left 4 dead 2\left4dead2\addons for manual addons, and workshop ones with \SteamApps\common\left 4 dead 2\left4dead2\addons\workshop. Tried doing that, same result happens again. I think I'm having same problem. Crash does not occur (so far) with Official Ded. servers.
Left 4 Dead 2 2009 Browse game Gaming Browse all gaming This video shows you how to join Left 4 dead 2 online with friends by using '"LAN Alternative App"'Local Area Network (LAN)

I see that Left 4 Dead 2 is the only game on your account so I'm going to assume that it's the game you're referring to in this thread. How to create a Lobby for a online match in Left 4 Dead 2. A private ( only-friends ) match or a public. Subscribe and get a free pie!

In-game multiplayer settings. Multiplayer types. Type Native Players Notes; Local play: 2: Co-op You can play Left 4 Dead over a local area network (LAN) connection.
To do this, go to your Steam library tab. Then right click on L4D2, and selet properties Next select the tab Local Files. The select Browse Local Files You will want to navigate to this folder C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\cfg If your Steam library is on your C drive, you can paste this string into your Internet Explorer address bar.
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how to play multiplayer left 4 dead 2