Since there is no simple way to perform a free unlisted phone number search, there is no guarantee that you'll be able to find a phone number that is not listed in the phone book. However, with all of the internet's resources at your disposal, your chances of successfully performing a free unlisted phone number search are much greater.
Your free unlisted phone number search should begin with a search engine that searches the deep web for personal information. One such search engine is pipl. If you enter the person's name, the deep web search engine will scour thousands of databases that are hidden from normal search engines to find any phone number information on the person.
The next step in your free unlisted phone number search, should be to gather useful information from the pipl search even if it doesn't turn up a phone number. Suppose pipl didn't find the unlisted phone number, but it did tell you where the person is employed. In this case, you could leverage this information to further your free unlisted phone number search. Check the company's website, perhaps they have an employee directory with contact information for the person you are seeking.
The last online stop in your free unlisted phone number search should be to enter the person's name in a search engine such as Google or Bing. You never know where someone might have inadvertently left their phone number; it may be posted in a forum or some other website where these mainstream search engines could find it.
If your free unlisted phone number search hits a dead end online, try some old-fashioned networking to try and find the phone number. You've surely heard of six degrees of separation-- perhaps a friend could put you in touch with one of their friends who has the number.