There was a similar issue reported in the Steam discussion
[Linux] Game won't start; check the fix goozler describes.
For multiplayer, have you tried using Direct Connection? You can use either an IP address for that or a 'Server ID' (which the host can get in the connectivity menu after starting or loading a game, by hitting Esc to bring up the menu to click that button, or clicking on the diamond icon at the top of the mini-map).
