There's no official discord, because I don't see a need for it. External chats are also difficult to moderate, especially when it comes to who-did-what.
There are chat-channels in-game (such as #main) to see if people are available for something right then and there. For other stuff, there's also the forums here, where - for example - I could tell you that I'm usually on at 3pm pacific if you want to do dungeons. Other people might have different times.
Most people are on in the evening, US time, though.
From what I can see, today was the first time you've been on after 12pm pacific. During the time you're usually on, most people in the US sleep, and most people in the EU are at school or at work. You could try coming on later?
Otherwise, the best way is probably to join with a friend - that's what the game was always intended to be, anyway. Invite friends, do stuff with them. Pretty much all dungeons can be cleared in 3.
The player base is what it is. There's no advertising, as the game's in development. ;) Getting a hundred people is a pain to moderate, and stressy. It can come once I'm done with adding content. ;P
