If you do not have the proper address of the harasser to effect service, you may make an application to the Court stating that you are unable to obtain the proper address of the Respondent despite your best efforts, and seek the Court’s permission to instead effect service through the Respondent’s email address or other electronic means.

For more information, you may refer to https://www.judiciary.gov.sg/civil/how-to-file-serve-protection-from-harassment