If the respondent does not want to be served, it is really not up to the petitioner to locate him. What the court wants is a concerted effort in locating the respondent so that later the respondent cannot say that no effort was made. Keep a journal of your efforts to show the court. Make an entry for every phone call, every address check, every mutual friend you talk to, every possible employer you contact, etc. You can relay this information then to the court as you learn about the individual's whereabouts, but it probably will not result in the individual being served.