The Sub-Reddit is here: https://www.reddit.com/r/SexMageWorlds/
I know it's not everyone's first choice, but Reddit is the easiest to go with. It's free, allows erotic content, easy sign up, is a pretty ubiquitous content aggregator, pretty basic and direct for posting, etc. It is not necessarily ideal for posting full stories due to its formatting, but people can submit links to other sites. Pastebin, Imgur, Blogspot, Tumblr, etc, are good places to host stories and images, so you can post your stuff there, and then link to the sub-Reddit.
I have also set up a Discord server: Invite Link
NOTE: Discord is NOT an IRC chat, it is a chatroom/group call program like Skype or TeamSpeak. The above invite is a link to get into the service, NOT a webpage with a set URL you can bookmark. You are supposed to create an account, authenticated by e-mail, and use that account on Discord as an app/independent program, even if you are using it in your web browser.
If you do not authenticate and use a set account, Discord will prompt you to keep making a new one, and each time you log in, you will keep creating duplicate accounts which can't interact with the server, and will end up adding empty accounts that bloats the user list. So please make one account and stick to it when joining the server.