Revenge porn is illegal in at least nine US states: Alaska, Arizona, California, Colorado, Georgia, Maryland, New Jersey, Idaho, Utah, Virginia and Wisconsin. In California, for example, this high-profile case is currently on-going:
http://www.ibtimes.co.uk/revenge-porn-website-owner-kevin-bollaert-faces-trial-over-explicit-images-1453139
The UK is in the process of passing legislation banning revenge porn too.