Maybe you can join some of the bigger gaming forums and start to share & engage in conversations with that community and usually after awhile they'll let you put a little promo or Link in your signature or some have sections of the forum that let you advertise your site. The Important is not to go in flagrantly spamming but adding some worth to the community by sharing and engaging. Also, as others have suggested you can find relevant groups, pages and profiles on social media and engage there as well. Make sure your tags, titles and descriptions are correctly filled to assure the best possible results. You also need to have a bit of patience as that is a very competitive niche.
Good luck on your journey.
