SECTION 7. Notice

If in such action the court finds that actual service cannot be, or has not been, made upon a defendant, it may at the request of the plaintiff order notice of the action to be posted in a conspicuous place on the land or to be published in a newspaper within or without the commonwealth, or both, or to be given in such other manner as it considers most effectual, and may also require personal notice to be given. Notice given under this section shall be constructive service on all the defendants.