Yeah, what she said. (As usual, huh?)
Back when there was a good-sized market for the short stories I was writing, the sweet spot seemed to be 3000 - 4500 words for print. Only big-name established writers were likely to sell a short story over 8,000 or 10,000 words. Anthologies' requirements vary substantially and depend on the anthology, its theme, and the genre. Most of my few anthology sales have been around 4500 - 5500 words.
I have sold very little to online markets, but my overall impression is their desired word counts are a little lower, more like 2500 - 3500 the ideal.
So what you've got is probably no longer a short story at all, but a novelette nearly novella size. When it's finished, you can seek specific markets for it at its present size, or see what (if anything) can pare the word count to make it eligible for more markets.
Maryn, whose short stories turn into novels far too often