Miami does not have a red light district per say. Prostitution is an illegal activity in the Florida, and Miami is not Las Vegas in terms of ignoring prostitution. You could pick up hookers on Biscayne Blvd at night next to the drug dealers. You can find fat, skinny, sexy, ugly, black and white prostitutes. There are hookers for everyone!
You can also find Miami escorts, streetwalkers, body rubs, strippers & strip bars, ts & male escorts from WikiSexGuide: http://www.wikisexguide.com/wiki/Miami