The websites, which source information from people looking for credit and sell this data on to other businesses, were found to be unlicensed and therefore in breach of the Consumer Credit Act.
These websites targeted people with disabilities, those connected to the military, and people with generally limited access to credit.
Following the investigation the regulator (OFT) is continuing to monitor the web to see whether the sites reappear with different web hosts.
David Fisher, OFT director of consumer credit, said: "We advise consumers to think carefully before entering personal data into any lead generation website, in case this information is passed on without their knowledge."
The 19 sites are: