Hi. I'm starting up a new group in Manhattan. I don't know where it will meet. I live in upper Manhattan, but could play somewhere farther south if someone wants to host there. I can't say what the demographics of the group might be yet. I just posted about it here.
My group is looking for another player for our 3.5 game. I know you specified 4e, however your other criteria couldn't be more spot on. We're a group of 20-30 year olds playing on the lower east side. In the near future we are likely to start splitting between brooklyn and the les, as one of our hosts just moved.
It's a bi-weekly game, and I have enjoyed it immensely. You can read more about it in our DM's thread: ta-da.