One of the reasons for a lack of tutorials is that there are way too many ways to do multi-player. It’s a very broad term that includes everything from a two-player turn-based game (think Words with Friends) to a near real-time game like Fortnite. It includes LAN/WiFi games to Internet based games.
Then there is the sheer number of online services that you can choose from. Google supports multi-player through their Google Play Game Services (GPGS) and Apple supports multi-player through GameCenter. Neither of these are cross-platform solutions. Gamesparks and PlayFab are two services that have plugins for Corona that you can use. You can see some additional plugins on our docs site:
https://docs.coronalabs.com/plugin/index.html#gaming
And in our Marketplace:
https://marketplace.coronalabs.com/corona-plugins?filter=category.slug%3Agaming&sort=%2BDate&all=yes
Any community advice is going to need to know more about what you want to do. Can you provide more information about what type of game you want to make?
Rob