I'd first think of what kind of demographic would your game appeal too. Do research on social media about other games on like twitter to see what other successful posts art like that you might be able to make note of. There is also Reddit and maybe a community for your kind of game. I'd recommend having a complete product or a demo page of some kind before posting on reddit. There are also forums that allow for created game posts, but I cannot think of one for mobile party games off the top of my head.
Social media is your friend.
I'm by no means an expert though, these are just a few things I'd do if I were marketing a game of my own.