Oh, OK. It is just that he won't reply because it is a gaming production company. I saw his name. He won't reply. Just leave the comment on his steam id account or something.
You can leave a long comment on the Developer's profile page as to why you would like to have a multiplayer option in the game or E-Mail them if the E-Mail is stated on their profile page. There's nothing any one else can do about it.
