If you’re looking to go out clubbing, then maybe the best choice for you would be to visit the Dover Street Market and see if they have any luxury girl dresses in your size. The likely answer is that they will, but if you can’t find it there then there are many premium shops around NYC.
If you’re looking for dresses for junior and senior prom, then I recommend checking out the Dover Street Market in New York, but if it’s anywhere else then I’m sure checking online for dress stores would help you out a lot. I actually had to find a dress for my daughter the night before prom.