If you want an example of an MV project with multiplayer online, there's one in development here;
http://afar.ws/
There's many ways you'd go about doing this, but you will need to write your own Javascript Plugins and you'll need to be very comfortable with web technologies.
Afar uses a mix of technologies, I believe the server-side is SQL based (which isn't good for real-time multiplayer, but it suits asymmetric multiplayer perfectly fine and you can make a very interesting MV project that way).
To do full-online, you'll need a real-time server-side, of which something like node with sockets would be best. You'll have to code the other players on the map yourself and you'll have to code the battle system from scratch and sort out what you want to be server-side or client-side and code all that again.
On top of all this, you need an account system, which will be a nightmare to code and will be a massive security risk that can ruin your project if something goes wrong, so what I suggest to most people is to use Google/Facebook/Twitter sign-in and let those guys handle the sensitive data, you just need to handle player data. Google's Firebase has this feature, as well as a real-time database so you can kill two birds with one stone; Firebase will cost money if you use a lot of data.
If you don't have the skills to do any of this, then I'm afraid you're out of luck. Either pay a professional a lot of money to do it for you, or wait for a clever individual to make a free, open-source Plugin that lets you create these systems with less of a headache (all the components are there, someone just needs to build it).
Online in MV is something that's very possible and is way easier than in older RPG Makers, but a lot of coding is required and you need to utilise a lot of different technologies. An online MV engine would make an excellent open-source community project, but generally the community isn't interested in online multiplayer with MV, let-alone open source community projects, so I don't see such a Plugin being produced any time soon.
If I had the time I'd love to do it myself.