Write a biography
Do you think you have exhausted all the sources available to locate your missing ancestor? Perhaps it's time to write that ancestor's biography. Write down everything you have found out about your ancestor. Do you know the birthdate? How about the location of the birth, the marriage, or the city where the marriage took place. Do you know the occupation? How about the siblings, or other relatives? How about the neighbors? Write all these things down and any others that you know. Then see if you can then create another research plan with these things in mind.