N.H. Rev. Stat. Ann. § 155-B:4

The order shall be served upon the owner of record, or his agent if an agent is in charge of the building, and upon the occupying tenant, if there is one, and upon all lien holders of record, in the manner provided for service of a summons in a civil action. If the owner cannot be found, the order shall be served upon him by posting it at the main entrance to the building and by 4 weeks' publication in a published newspaper of the municipality if there is one, otherwise in a newspaper of general circulation in the state.