If you have found yourself looking for a particularly hard-to-find person, and both the free and professional search sites are unsuccessful, there are some additional ways to search for people, but they often depend on additional information about the person you are looking for.

First, what sort of information do you know about the person?

An old phone number, address, even email can often be used to help find someone with what is known as a "reverse search". A reverse search allows you to use the information that you have (ie phone, email address, etc) and to search for related information such as the whereabouts or additional phone numbers for the person you are searching for.

Like the professional people searches, these too come in two types. A single search version and an unlimited search version. For example, Spokeo.com offers unlimited searches for an annual fee. While other sites like Intelius.com sell searches individually.

If a reverse search is not successful you may consider the social networking and personal sites. Nearly 30% of internet users have personal information on a social network or a personal websites.