Taking a random look at published, publishing (ongoing) stories on the site, you can't help but reach the conclusion the number of readers is very small. The best an author might hope to achieve, is 1000 page views per chapter.
Certainly, when you look at these numbers casually you see some large numbers, but look a little closer. A series author jdonley has written over 800,000 words in four books over several years and the number of readers is around 1000 page views per chapter per year. The numbers only look big over time.
Take a well know author personality, Comicality, the numbers are ten times smaller and he has been writing online for over twenty years and writes about writing. I suppose if you add up all the numbers multiplied by the number of stories, you get some high figures, but divide them by chapters, by years, and it's miniscule! One book, on going, over ten years achieves 100 page views per chapter per year.
Conclusion, the site online community is very small in terms of readership per author per book, what it achieves in site numbers overall is through the number of authors publishing as displayed on the front page. 100 page views per story chapter multiplied by 100, 200, or 1000 stories adds up, hence the site can support itself, advertising and premium membership.
For the author, you need to be realistic, you may receive several chapter comments and a few (not very balanced for the most part) reviews, if you complete your story. You can have some contact with other authors and readers, which is not to be underestimated and can be valuable, but if you are thinking you will achieve any sort of real readership (as in a print addition from a publishing house) you are mistaken.
In brief, being realistic, it is a lot of effort, hours of writing, a big investment, for very little return. Of course, nobody will tell you this and you can convince yourself you will get, or have, a large readership, but the numbers tell the real story.