There are ways around that -- Here in Alabama, the procedure might be different but I wanted to share so that you can understand that there is a legal path.
I was told to have the person served at the last two known addresses. And when that doesn't work, I would have to file a motion to the court and ASK permission basically to have a public notice published in the local paper here and where I think the person might be for three weeks in a row.
And then.....move forward.
But your state and procedure might be different.
The clerk at the court can't practice law for you, but sometimes they can answer procedural questions.....fine line, and that's who helped me. (No not against EX#2....someone else.)