The plaintiff must cause a notice to be served a reasonable time previous to the day for appearance before the referee appointed as provided in the last section, on each person having outstanding liens of record who is not a party to the action, to appear before the referee at a specified time and place, to make proof by his own affidavit or otherwise, of the amount due or to become due, contingently or absolutely thereon. In case such person be absent or his residence be unknown, service may be made by publication or notice to his agents, under the direction of the court, in such manner as may be proper. The report of the referee thereon must be made to the court, and must be confirmed, modified, or set aside and a new reference ordered, as the justice of the case may require.