Check out these guys,
http://bitcoinnyc.org/http://www.meetup.com/bitcoinNYC/We are a volunteer group of Bitcoin enthusiasts who want to help foster and grow the NYC Bitcoin community. We host discussions every Thursday at 6:00 PM, with each week focused on a different topic. You can stay up-to-date with event times and locations by joining us on Facebook or Meetup.
We look forward to establishing a vibrant community here in NYC, and hope to see
you all at our next meeting!
An interesting article about bitcoin trading in union square park:
http://www.coindesk.com/nyc-park-becomes-real-life-market-for-bitcoin-trading/I personally use coinbase.com for all of my buying and selling.