I find that multiplayer games are way harder to find people.

people see it, and don't want to play the game, is there any way I can make people want to try it at least?

also another problem is that they download and never play again, or with another person. the multiplayer solution doesn't use public lobbies. you have to join with a code that the host can hand out.

if you want to check my games page and see if you notice anything that is stopping my game from finding people https://snapgamesstudios.itch.io/kingmaker-test-build

edit: nevermind - I misunderstood and didn't catch it was about marketing  sorry 😓

technically multiplayer is very easy as you just send packets with UDP and hope it arrives
and it's possible to set up some peer to peer thing very quickly

but one very large problem nowadays is the security - players sharing their IP is asking for trouble 🤔
so for security reasons it's better to have a server inbetween - to at least hide the IPs
but even a small server costs a fortune
(even nintendo is using some amazon cloud service thing for splatoon - and that is only matchmaking)

so I kind of given up on it myself  😓

there are some strange options:
one interesting feature steam has that it lets local multiplayer games streamed to other players as a video stream 🤔
(but I don't know the details just heard of it)

and there is the option to write the whole thing in roblox - and possibly in other popular netgames
where they already have the whole server thing set up 🤔

You need to invest in it, if it's a good multiplayer you should make a lot of money. Make sure to market before the release, at least a month or so prior.