Once upon a time, for a very long while, I interacted with fandom pretty much exclusively over LiveJournal (and later also InsaneJournal and Dreamwidth). Then I decided I wanted to be FAMOUS ON THE INTERNET so I went and spent 5 years doing shit in the "That Guy With The Glasses"/online video reviewer community. Then I sorta dropped ALL OF THE BALLS and became a professional alcoholic for 2 years. Then I totes got sober and have been trying to figure out wtf even is life and myself and my mental issues and whatever for the past 2 and a half years. During that time, LiveJournal became RussiaJournal, my old RPs and RP pals moved on, the reviewer community divided by zero and spawned infinite fractal points with no real uniting hub or community anywhere, I forgot how to enjoy things, and then... I started re-learning how to enjoy things but have NO. FRACKING. IDEA. how to fandom anymore. SO HERE IS A POST FOR "WHERE THE FUCK DO YOUR FANDOMS LIVE?" Reveal to us where we may go to engage in fandom shenanigans of all kinds out there in the cyberspace jungle. Feel free to post links or talk about how to find/jam with your specific fandoms. ^_^
hmmm, i do a lot of fandom stuff on here, but that's pretty small-scale! if you can brave the discourse, tumblr is where i get most of my fanart, meta, and memes--it's mostly an art of following the right people and using blacklist and post block liberally for fanfic, ao3 is really good, and the sort-by-kudos feature generally generally lets you weed out the crummy ones HOWEVER, for a livejournal-ish feel, i think dreamwidth would be up your alley? it's run by the same folks who do ao3, and there's probably a place for just about every fandom you could fancy, but i don't use it much so unfortunately i can't help here ):
i think fandom mostly lives on tumblr these days. archiveofourown is also a popular fandom spot, though it mostly contains fic. and there's rping on dreamwidth, with plurk as the place where ooc discussion happens.
IME Tumblr is pretty good for fandom but is really lacking when it comes to smaller fandoms, and you always run the risk of anti crusades
I find Tumblr near-impossible to use as a platform to interact with fandom... at least I've never been successful at making any friends or building any sort of reputation for myself in any of the fandoms I've pursued on there. Examples of the most active ones I've been in on there are Welcome to Night Vale, Steven Universe, and Elder Scrolls. I still reblog a lot of Elder Scrolls stuff -- I still haven't befriended anyone but the content is mostly very, very good. Also I run a Jeremy Irons fan blog. Or two. >.> I've found Reddit to be the actual best place for Elder Scrolls fandom the way I'm interested in interacting with it, which is primarily as a lore scholar. I'm really bad at using Reddit though and the TESLore forum is literally the only Reddit forum I know how to keep track of... by keeping it open all the time. \o/
Antis are annoying people, usually kids, on the internet who get in a moral huff about art they have deemed morally suspect, usually for insane reasons, and they harass and threaten fans of said Bad Things
Fandom as a whole isn't super active on DW, unforturnately; when LJ starting dying most people migrated to Tumblr instead. DW's been stuck in a "well we want to use DW for fandom but nobody in fandom uses DW" purgatory for a years. It's still popular for RP but that's about it, has been my impression. Meanwhile I am eagerly awaiting the day fandom migrates away from Tumblr because ughhhhhhhh.
Ah. I... think I have seen that happen once or twice? Always in Night Vale fandom. It was a long time ago. I am surprised at how people talk about Tumblr fandoms being full of drama, but I'm always like "...where? Where is this drama happening? Not the hell in any of the tags related to fandom..."
Lucky duck. I happen to really like a work thats getting trampled rn. Its obnoxious. A majority of the main tag is people preaching. Fan blogs literally say stuff like "I look in the tag so you don't have to" because it's such a shitshow And its like, i can always step away from it, and I don't feel threatened or anything, but it makes engaging with fandom really difficult when this happens, because you want to see art and meta and it's just wank out the wazoo.
Additional input since I realized I didn't actually answer the main question: Tumblr is the main general hangout place, so when in doubt try there -- it'll pretty much always have SOMETHING for your fandom. AO3 is the undisputed king of fanfiction. Authors will often crosspost to Tumblr or elsewhere, but basically everything's hosted on AO3. Twitter is pretty good for anime fandoms, especially fujoshi-type stuff. Lots of shitposting, fanart, and group screaming/crying/rejoicing when new things happen. Reddit is really good for video game fandoms. It's mostly sharing information/experiences, discussing strategies, and posting dumb screenshots. Occasional fanart but not that much. Dreamwidth is for mostly RP, like I said before. Also anon memes -- kink memes are there (I haven't done kink memes in a while, so I can't say much about them), and fail-fandomanon's still going strong as the big general anon meme. Past that it varies a lot by specific fandom and you kind of just have to find stuff by poking around. A lot of fandoms have their own forums or wikis that people congregate in. Like the last big thing I was into was Stardew Valley, and it's mostly on the official forums for the game + Tumblr.
On Tumblr, don't expect to get noticed a whole lot unless your fandom is small enough that a new person in the tags is a noticeable event or you're actively creating content for that fandom. Also Steven Universe fandom: DON'T. just don't, its one of the worst currently with people getting mad and declaring X to be Problematic whenever anything happens.
Also just ask people in the fandom who are some cool folks to follow! Or if you see art or writing you love, follow the artist and let them know!
Today my wife told me about some SU fandom wank on Tumblr and I had to stop her twice because the portmanteau ship names were too overwhelming for me to be able to follow anything she was saying and drive at the same time. Her story involved a war between people who ship Lapis/Peridot and people who... uh... don't? Possibly specifically somehow this involves people who ship Amethyst with either/both of them??? It made my brain hurt. A lot. I've never understood people who fight over shipping, though. I literally cannot understand how anyone's preferred pairing can be actively harmful or antagonistic to anyone else's. Also it's fucking boring.
Yah but this has never resulted in my getting to know these people or having conversations with them. Except a few times when the conversation was them messaging me to tell me to piss off out of a thing they were talking about with someone else. :|
ACTUALLY... I fucking love some good fandom drama. I am deeply, deeply sad to have discovered that the FandomWank journal has been wiped off the internet. Some of those tales were CLASSIC, some were ones I'd barely missed being part of, and pretty much all of them were a guaranteed good show.
I'd try fail-fandomanon on DW for this! My friend who hangs out there says it regularly has threads for laughing at the latest Tumblr wanks and other internet drama, plus it generates plenty of its own wank for lurkers to popcorn.gif at.
For the SU fandom, the SU subreddit is actually pretty chill, I've found? I don't spend much time there but it's a lot less Unbelievably Fucking Horrifying than the Tumblr SU fandom. (ALSO IF YOU HAVE SKYPE HMU I WILL ABSOLUTELY RAMBLE ABOUT SU WITH YOU) And yeah, AO3 is the best place to look for fic (and post fic, if that's your jam). I could give you some fic recs for SU, though I'm not in the other fandoms you mentioned so I can't help you there (though I DO have a few really good friends who are active in the WTNV fandom and could probably recommend some stuff)?
With TES you definitely might have more luck in the various subreddits. Some are dedicated to the games in general, ones to specific games, some to lore or deep lore, and some to mods and such. So depending on what your poison is with Elder Scrolls you should be able to find a subreddit dedicated just to that.
Oh, I'm a veteran of TESLore from way, way back. I've got my share of Scholar of the Week scout badges on Reddit, archived appearances in the Bethsoft forums, and a little piece of canon one of the writers named after me. ;)