Hey! I've been looking unsuccessfully for websites similar to literotica.com, with erotic stories written and rated by users, but in Japanese. I figured it'd be good practice to read some in Japanese, but I have no idea what to search for using google, since English searches don't yield any results and I lack the respective Japanese vocabulary.

It would be great if someone could point out some websites with good stories or maybe some other source of written erotica in Japanese.

大人のケータイ小説 seems to give reasonable hits. ケータイ小説 are a category of novels written to be read in short bursts and were formatted and published on sites formatted for smartphones. Some of these stories were eventually published in book form but retained their short chapters, fast story pacing, and simple language.

Wikipedia has a but more information and the Japanese article is of course much bigger: Cell phone novel

Dan Oniroku (団 鬼六) is considered one of the best Japanese erotic writers. You can find a lot of books written by him.

I found otona-novel.jp thanks to your suggestion to search for ケータイ小説, tokyostyle. It's pretty much exactly what I was looking for, and there also seems to be a reading app for android.

I'm glad you brought it up. I had forgotten about them completely which is sad because they are so rewarding to read. In case you want to dive into some of the slightly softer stuff a large collection of them was released on the PSP as みんなで読書 携帯小説ですぅ~.