A. Upon the filing of an affidavit by a duly authorized officer, agent or attorney for the petitioner stating that he believes any owner cannot be personally served because after diligent inquiry within the Commonwealth such owner’s place of residence cannot be ascertained or, if ascertained, that it is not within this Commonwealth, service of the notice may be made on such owner by an order of publication. Such order shall be published in a newspaper published in the county or city where the property or major portion thereof is located, or if there is no such newspaper then in a newspaper having a general circulation in such city or county, once a week for not less than two successive calendar weeks and shall be posted on the front door of the courthouse within 10 days after the entry of the order of publication. Unknown owners who may have an interest in the property may be served by order of publication in like manner addressed to “Unknown Owners.” The clerk shall mail a copy of the notice by publication to any owner who cannot be personally served but whose place of residence is then known.