Can I invite my Steam friends to a party/match?
Yes. Once connected to the server, any player can invite other players through the Steam overlay (shift + tab). This applies to both public and private matches.
If you have Steam friends who are online and in Streamline parties that allow Steam friends to join, you will see a “FRIENDS” button on the home menu and the number of friends you can join. Clicking this button opens a display that gives you a list of options to join your friends’ parties!