Like others have said, just ask on the forums for likeminded players who want to play coop with you. Then you guys can hash out a time and date, etc.
I've been on the other side of what you have went through but I didn't use any name calling. I was playing with 3 friends and a stranger jumped in during character creation (you can't set the game to private before character creation, I've tried). My friends immediately wanted him kicked but I gave him a chance. We got semi-far but the way he played just did not mesh well with us (We're quick and each have our set paths on how to progress, while he took his time. Not his fault, just didn't mesh with our style). After I kicked him though we were stuck with his character (please address this Larian)!
But yes, searching the steam forums or even here for potential coop partners is a good start as you can list what/who you're looking to play with.
