Take the plastic flea collar off and check around her neck - is the hair missing? The cheap plastic Hertz Collars often burn the fur off as the med is too strong and it can poison the cat as well, this is common with deli cats and other neglected kitties. There's a nutty mentally ill woman near where I lived who liked to put these collars tightly on the local strays to "claim" them but they weren't hers - so having a collar does not necessarily mean a carer.
However you can also check on Tabby Tracker - you can post her as found as well.
Whatever you do don't take her to the AC&C as they are a high kill shelter.
Try calling local rescues to see if anyone has any space for her if you cant find her owners. This time of year is very busy as it is the end of kitten season. She will need to be blood tested and vaccinated to ensure she is healthy and neutered but this can be done for little to no cost through Toby Project and/or ASPCA's Public Mobile Van's.
Some local shelters you can try calling are:
Sean Casey: http://www.nyanimalrescue.org/
Bobbi & The Strays: http://www.bobbiandthestrays.org/
There are loads more if you look, some of the smaller groups may ask for a donation to cover vetting costs.