RCW 16.04.050

If the owner or keeper of such offending animals is unknown to plaintiff at the commencement of the action, or if on the trial it appears that the defendant is not the proper party, defendant, and the proper party is unknown, service of the summons or notice shall be made by publication, by publishing a copy of the summons or notice, with a notice attached, stating the object of the action and giving a description of the animals seized, in a newspaper of general circulation in the area where the plaintiff resides less than ten days previous to the day of trial.