I'm trying to reward players for giving my game a thumbs up or favorite but I don't know how to find the players liked or favored games.
Hello. That's actually against ROBLOX Rules and Terms of Service. Awarding players for favouring or liking your game is against ROBLOX Rules and Terms of Service. You can incite players in a non-abusive way to like and fav your game, but not to reward them if they do so. Here you have the ROBLOX community rules: https://en.help.roblox.com/hc/en-us/articles/203313410
EDIT: An extract from Roblox Community Rules, more specifically...
Do not create promotions offering prizes of any sort(including contests, raffles, lotteries, chain letters or any kind of giveaway). It is okay to offer players promo codes for in-game items only so long as they are not in exchange for something (e.g., in exchange for a thumb up on your game).