RCW 7.52.050

If a party, having a share or interest in, or lien upon the property, be unknown, or either of the known parties reside out of the state or cannot be found therein, and such fact be made to appear by affidavit, the notice may be served by publication, as in ordinary cases. When service is made by publication, the notice must contain a brief description of the property which is the subject of the suit.