Is it? I really want to set one up.
A while back the “Create Multiplayer” button was moved, but you can still create them.
Hit “Start New Game”, then select the map you want.
Hit the small wrench icon near the top right to edit any settings such as sandbox limits and the name of the listen server.
After you selected the map and modified any settings hit “Start Multiplayer” and be sure you opened the ports on your router / firewall (default port is 27015), use a site like http://canyouseeme.org to check if the ports are open and be sure you give your friends your WAN ip to connect with not your local ip use a site like http://ipchicken.com to find your internet ip if you don’t know it already.
look into hamachi as well. It’s really good for setting up private servers