There are plenty of hollowed out cities, abandoned and waiting for fresh life.
Make a call to flight of every able bodied, worth while, individual to flash mob one of them and start
making it live...
'Lets all go to Detroit'?
...
You know, that actually sounds like a good idea. We'd need to get the entire social structure set up beforehand, though, and just put it into place once we get there. Basically, like Astro said, design the city online, and once we have enough people to constitute a 'skeleton crew' of a city, we start moving.