Most fanfiction is set in worlds made popular by television and movies. Some popular worlds include Anime, Final Fantasy, Harry Potter, Star Wars, Pokemon, Overwatch, Game of Thrones, Twilight and Supernatural. Below you will find some resources about fanfiction and some popular fanfiction sites.
Commaful
Commaful is a site for reading and sharing fanfiction as well as stories, poems and comics. The site has a picturebook foramt.
FanFiction.net
A dedicated fanfiction site with multiple categories, genres and discussion forums.
Fanlore
Fanlore is a wiki about fanworks and fan communities.
FictionPad
FictionPad lets you read and write stories in your favorite fandoms.
FicWad
FicWad is a fanfiction site. Celebrities and anime/manga are two of the most popular categories.
Fifty Shades of Grey Fan Fiction is Booming
An article about the growth in Fifty Shades of Grey fanfiction.
Inside the racy, nerdy world of fanfiction
This CNN article acts as a fanfiction explainer with site links, facts, lingo and information for parents.
Kindle Worlds
Amazon launched a digital publishing platform to enable writers to create and sell fan fiction.
Mary Sue Characters and Tests
Check and see if your beloved fanfiction character is a Mary Sue.
MediaMiner
This fanfiction site has a focus on anime and game-related fanfiction.
Quotev
Quotev is known for its quizzes but they also have stories and fanfiction in multiple genres.
r/FanFiction Reddit
A Reddit for the sharing and discussion of fanfiction.
The Ultimate Guide To Fanfiction and Fanfiction Sites
The Medium article reviews some fanfiction sites and types of fanfiction. It also gives advice to fanfiction writers.
Wattpad Fanfiction
Wattapd is a writing community with a large amount of fanfiction. The link goes to Wattpad's fanfiction reference guide.
WhatTheFanfic Reddit
A Reddit that discusses fanfiction published online.
Wikipedia Fanfiction
The Wikipedia entry covers types of fanfiction, related terms and the legality of fanfiction.