I am not admitted in Washington.  You should seek legal help in your area to petition the court to remove the executor on the grounds that he is not fulfilling his duties.  If the attorney for the estate can not locate him then your chances are probably just as slim.  You will need to give hime some type of notice (probably through publication) after doing a "due diligence" search for him. 

At the same time that you poetiton to remove him request that another be appointed in his place to complete the estate.  Two things can happen here: you will find the executor and show him you mewan business which may prompt him to act or you will have a new executor to finalize the estate. Good luck.

I am a Washington attorney, and the advise you already received, about removing the executor and having the court appoint another executive to close the estate, is correct.  The one problem will be locating the current executor.  If you can't find him/her, you can publish a citation to come to court for the hearing to have him/her removed.