If you want to report any sort of child exploitation, you can either contact your local FBI field office (they are in the phone book), or file a report with the National Center for Missing and Exploited Children (
http://www.cybertipline.com), who will forward it on to the appropriate authorities.
You should do whatever is necessary to clear your conscience in such matters, there is no "deal", as simply searching for something is not necessarily against the law regardless of how offensive it is to you. As long as you have no illegal material on your site, you will not be held accountable for such searches landing there anyway. It could easily be a fishing expedition as well - i.e., an agency or watchdog out searching sites for illicit material.