Some communities do indeed work! We don't use them much ourself, so are useless for recs, but there are some still plural comms around. (By which I mean, like, proper ones. pluralstories is kinda monkeywrenching it for cataloging purposes, it's not really a social community!) Search "plurality" or whatever as an interest (it's in the search bar in the top right corner) and at the "Show:" list, click "communities only." (You can also use this to find individual users with interests you share, be they "plurality" or... I dunno, "macrame.")

Finding people on Dreamwidth is generally having conversations in the comments! Find people in the comments saying neat things, respond, check out their accounts, see if they're saying interesting things, then comment there and say hi and see if you hit it off. Tags are PURELY for individual blog sorting and have no global search. (I honestly way prefer this; I don't want to have to come up with weird workaround names for my tags to avoid people searching them globally just to be a jerk to me! And it also means nobody'll get spammed because I'm using a "plurality" tag and doing a bunch of catalog work for it all at once.)

You can also check out people's profiles to see if any of their comms or friends look interesting!

But yeah, commenting is the main name of the game.