If you're seeking an old friend but only have an out-of-date phone number, you might have a little legwork to do. It might take two or three online searches, plus some investigative work on your part, but it's possible to find someone with only an old number.
Search the number via Google. (There is a link in the References section.) Enter the number in the format 555-666-7777, press Enter and review the results.
Check what's associated with the number in Google's listings. The number might be associated with a business or organization, people's names, posts on social networking sites and blogs; all of these are viable contacts for you to investigate. For example, if the old number is listed on someone's MySpace page, send a message to that person, explain who you are and ask if they know the person's current contact information.
Conduct a search in an online database. Enter the phone number in an online people search database, such as Pipl -- there is a link in the References section -- and see what information is connected to that number. For example, if the number appears on a website or blog, contact the webmaster or blog owner and request current contact information.
Run a reverse check on the old phone number. Enter the number in Phone Validator (there is a link in the References section), which displays the location for that telephone carrier. Dial a 411 directory assistance number, such as 1-800-FREE411, ask for listings for the person's surname in that city and call those numbers. You may find a relative who can give you current contact information.
Hire a private investigator. If you hit a dead end, it might be time to pay for the services of a professional. To find a qualified PI, contact your state professional private investigator association, ask friends for recommendations or contact attorneys and request recommendations for PIs who specialize in locating people.