http://www.coolfinder.com
is an on-line telephone directory which might help, if your person has a phone. Or try simply typing their name onto Google search. It's surprising how often non-famous people can be located.
Good luck.
You might be able to use an inquiry agent - basically a private detective. If you can't find one on the Yellow Pages, try asking a high street solicitor for a name of an inquiry agent they use. Of course, you would have to pay the agent's fees.