Sorry, there's nowhere on Chrons for non-Supporters to share the whole of a longer story, though it is possible for someone who needs help to put up a, say, 4k story by means of 3 Critique threads over the course of 3 or 4 weeks. However, Supporters have the advantage both of the Writing Group where stories of any length can be posted for feedback, and of the Supporters Blogs area where any creative writing can be posted as part of a blog.
Otherwise, are you part of a writing group? If not, I'd suggest you look around and try and find one, either in real life or online. If you find a good one, that will give you both a readership and continuing help with your writing as you progress. Finding a good one is the key, though, so be prepared to meet with some which are sub-optimal, and leave them if they're not helping you enough. Meanwhile, perhaps ask if anyone here is willing to become a beta-reader for the story -- you never know, if you and the reader hit it off, you might start a writing group of your own! (That's in effect what has happened here on Chrons for a number of people.)
There are outlets for longer short stories, so do investigate these. If this is one of your first completed shorts, though, and you've not had it fully critiqued by people who know what they're talking about, to be frank it's unlikely that a paying organisation is going to take it straight off the bat -- competition is fierce. So rather than submit a story which isn't perhaps ready, I'd counsel you to hold fire for a little while until it really is as good as you can make it. Otherwise, if you're not interested in being paid, there are places which accept stories without payment -- and therefore without any editing or requirement for quality, so the other authors on the site might not be up to your standard, and any feedback you get might be in effect worthless.
However, if you're not worried about payment, I think your best bet is to get your 30 counted posts then put up an extract of the story here in Critiques, with perhaps a follow up a little while after, then use that as a springboard for asking for beta readers, and see what that brings you.
