Hi there, Vigda! Welcome.
I live in NYC also. There are a couple of poly groups in NYC. They're growing but not huge. The poly events I went to were nice, for the most part, with a wide range of ages in attendance. Here are the groups I know about
Open Love NY
hosts lectures and a monthly cocktail party on the second Monday of each month called... Poly Cocktails! These draw anywhere from 40 to over 100 people. They're usually held at a bar on Avenue B. Next ones are Nov. 14th & Dec. 12th. The lectures always look interesting, though I've not attended one yet due to scheduling, but I have been to the parties, which are about socializing and meeting people. I like the people who run this group, a great and welcoming bunch.
Their website is here (you can sign up to be on their mailing list): http://openloveny.com/index.html
There's also the New York Polyamory Meetup Group
. They meet twice a month in Manhattan, on the second Sun. and fourth Thu., and they also have a Westchester branch. I believe their get-togethers are usually "munches" at restaurants where they talk over dinner. I haven't attended any of theirs yet.
Their Meetup page is here: http://www.meetup.com/New-York-Poly-Meetup-Group/