Where is curbcrawlers in GTA 4?

Answer 1

If you mean the drivers who "kerb crawl" whilst looking out for hookers, all you have to do is cruise around Liberty City at night, and where hookers are congregating for business, you will find drivers slowing down to talk to the hookers, and so kerb crawling.

There is an area next to Niko's safehouse in Bohan, right on the corner to the left as you come out of the front door, where hookers stand on the pavement there.

Also, still in Bohan, in the area behind Niko's safehouse, on Chase Point, almost the whole of that area has hookers on the pavements looking for clients.