N.H. Rev. Stat. § 498:5-b
In any action brought under the provisions of RSA 498:5-a, if the plaintiff therein alleges that there are or that he believes there are or that there may be persons who have or may have some estate or interest in such real or personal property, but such persons cannot be located and are unknown to the plaintiff, and describes the actual or possible estate or interest of such person or persons, and how derived, so far as may be known to him from the available land records or otherwise, or if the party who may have an interest or estate in such property is a corporation whose corporate existence has been legally terminated or such corporation is no longer in existence or doing business, and in the complaint the plaintiff describes as parties defendant "the unknown persons who claim any interest or estate in and to the subject matter of this action," it shall not be necessary to set forth therein any further description of such unknown persons. If the plaintiff or his attorney annexes to the complaint in such action an affidavit setting forth such facts and in addition sets forth the efforts which were made to ascertain the names and addresses as well as the interest or estates of such unknown persons, the court to which such action is brought may make such order relative to the notice which shall be given in such cause as such court deems reasonable. Such notice, having been given according to the order and duly proven, shall be sufficient to confer jurisdiction of all such unknown persons and the court may proceed to a hearing of the cause at the first term or session, or afterwards as it deems proper. Such court in its discretion may appoint any guardian or other person to represent such unknown persons under any legal disabilities and all such persons shall be concluded by any decree or judgment in respect to the real or personal property involved in such action.
RSA 498:5-b
1971, 292:1, eff. Aug. 22, 1971.