Official Multiplayer:
If you're having trouble finding a multiplayer game or need help with hosting, consider the following:
You need to "trick" Steam into thinking you are playing a different, legitimate free game so you can use its networking. client and log into your profile. Windows + R on your keyboard to open the Run dialog. steam://install/324810 (this is for TOXIKK) or steam://install/480 (for Spacewar) and hit OK. Let it start the download for a few seconds, then