My response:
Oh my gosh ! You could have saved a lot of money and time !
The law does not require you, as a Petitioner or Plaintiff, to jump through difficult hoops or hurdles to locate someone in order to divorce or sue that other person; i.e., the law does not require a litigant to hire a private detective, or the like.
All the law requires is that a "reasonable, diligent, effort" be made to locate a missing potential litigant. That means, phone calls to the Tax Assessor's Office, the Department of Motor Vehicles, the Post Office, and other places who might have "location" information. If those agencies do not have such information, you have then completed your "diligent efforts".
Once that "effort" has been made, a Motion can be filed with the court to obtain the court's permission to Publish the Summons and Petition in a newspaper of general circulation in the town where the "missing litigant" was last known to have resided. That's it, and then you have completed your obligations to give Notice of the pending litigation.
If the other party see the Legal Notice in the newspaper, great. If they don't see it, that's tough.
IAAL