I'm assuming you're applying through BUNAC or a similar programme in order to obtain the visa, I took part in Work America last summer, and I had a job lined up before going to America, most people do.
As for getting a job once you are there, if you are using BUNAC then they can provide help once you are there also. Otherwise I would recommend getting a job before hand, especially in New York, but i guess it depends on you - if you feel comfortable going out there without a job. Im sure there are lots of jobs going, just have to know where to start.