Many of the people on "To Catch a Predator" were charged with "Criminal solicitation of a minor" (or similar charges, as these are usually state charges and can vary from state to state).

Most of these charges contain a clause that reads - or is similarly worded to: "if he/she knowingly contacts or communicates with, or attempts to contact or communicate with, a person who is under the age of xx"

By this definition, it is not required that the person actually communicate with a minor, merely that they attempted to do so (usually by believing the person they're contacting is a minor and continuing to solicit them anyway).