Cannot connect to anyones’ game and according to the Steam forums I’m not alone in this.
Please fix or my weekend is ruined. 
Are you using the Friends list? Try searching for the game name?
If that’s works, Steam’s friends list may be fritzing out right now.
Not a single public game shows up even, so I’m not sure what exactly the issue is tbh.
I’ve been having similar issues as well. After going at it for a while it might start working again, but it’s been problematic.