Moving to the author's lounge as this main section is for posting the actual story, not for asking for writers.
Note though that it's not too likely to find someone (mostly people interest in writing fics tend to already have their own projects), and co-writing is not straightforward either (what if the writing styles or interests/genres clash, or one writer is not as good by the other, for instance). Ideally you'd probably want to include more info too, such as how you write, what exactly you are interested in writing, etc.