Wis. Stat. § 94.31: Service of notice.

In all cases arising under ss. 94.26 to 94.30 when it shall be necessary to serve any notice upon any person who may be out of the state or whose whereabouts shall not be known to the person desiring to serve the same, such notice may be served upon any agent or employee of such person who may be found within this state, and such service shall have the same effect as if it was made upon the party interested.