Reddit is great for getting game players because it has pages, called subreddits, dedicated to game players.
Colin mentioned buying ads, but you can also do it the manual way. If your not on there already, first spend quality time on there, joining subs you find interesting and posting comments and question posts. Build up karma by posting questions, pictures, devlogs, anything with no links. After you've got around 500 to 1k karma and get the feel of the place, then start to post link posts, typically you want to only post 1 link post per week.
The main game subs that are for posting links are; webgames freegames playmygame destroymygame playtesters webmobilegames. And itch has a sub too.
You can post a link to your game on each one, but you should not post to all of them on the same day. Wait about three days to a week in between posting the same link to multiple subs, or have different links, like one to newgrounds one to gamejolt one to indiexpo, and wait a day in between posting each link to the subs.
Other subs more for like devlogs are solodevelopment gamedev gamdevscreens.