Most Pixiv users are Japanese, so it's probably going to be more difficult to find readers there than other sites where there's an English-speaking majority. Like DeviantArt, it's also a more visual art-focused site, so getting traction for novels there is probably even more difficult.
I post art on Pixiv, but I would not think to post my writing there, even if I ran it through a translator. When it comes to translating novels to any other language, you really have to consider how things like prose and idioms will (or won't) work, and machine translation often won't cut it.
