Yeah, promotion is a huge task in itself. From looking at your itch profile, I'd suggest three immediate tips:
1) Create a striking game thumbnail that isn't just a screenshot
2) Make an avatar
3) Have at least one social media account that your profile links to.
Stop worrying about big budgets- that's not going to happen easily for any of us! Think instead about what you can do yourself. It's worth asking who do you want playing your game, and why aren't they playing it at the moment. If you hadn't made the game yourself, would you even know it exists and- if not- what can you do to change that?
Going from zero to multiplayer *is*, however, an almost impossible task. Can the game be played single-player too? If not, you need to introduce this otherwise people will just look at it, have no one to play against, and go. Just realised this point is pretty much what PaulsGames above me said so... yeah!