Until they are found or until all resources have exhausted and it has been determined that the person is either not in the area or is deceased. If new information is developed the search can be resumed or handed off to another agency if it is believed the person/s are no longer in their area of responsibility.

The obvious answer is: as long and as hard as it takes to find the person. But this is one of those questions that can't have a standard answer. The ideal would be that a search goes until the person is found. However, the intensity and duration of the search is determined by a tremendous set of circumstances that are too long to get into here.

I work in a park and I have had S&R training and have been involved in several searches, and I know that the persons who are involved will work themselves to exhaustion to try to find a missing person. And at the report of a missing person a chain of events is triggered that will bring out all the resources available in an area as quickly as possible. Searching will continue until every inch of a park (and the surrounding area) has been searched, evidence indicates the person is somewhere else, the search resources are exhausted or the person is found. Intensity is usually highest at the beginning and wanes as time goes on based on whether new information is found or not. And even if you get to the point where additional resources for searching are not available, every park staff person in that area will be looking as they go about their duties until a conclusion is reached. We don't like not finding a missing person.

So, even though an official search is called off because of one of numerous reasons, it may never end in the mind of a park ranger.

The search should go on intensely until all hope of finding the person alive is exhausted, based on weather conditions, how much food, water, shelter they had with them, etc. After that, as time and personel allow. An exception to this would be if there is some indication that the person may have been murdered and finding the body would yield evidence to bring the perp to justice.

I once met a ranger hiking the back country of Sequoia. He had been hired by a family to search for the body of their son who had gone missing while cross-country skiing the winter before. I cannot imagine a grimmer task.

Sometimes family and friends can get unrealistic about how much effort and danger that should go into a search. It's their loved ones, but it's also someone else's loved ones conducting the search and perhaps putting their own lives at risk.

I remember after the big Vernal Fall incident last year, the families of the deceased laid into NPS for not continuing the search efforts that night until they were found. They held out hope that their relatives could have survived the initial fall and hadn't drowned. Sometimes reality doesn't necessarily kick in, and some want to wage efforts that aren't necessarily warranted.

When people leave notes, as in the case mentioned in the smokies above, indicating they do not wish to be "rescued", I think the game is changed. The predominant sentiment here is that these guys were one, wanted by the law and used this to throw them off their trail, and two, trying to achieve a Bear Grylls status. Either way, it is a waste of taxpayer money to go hunting for dubious folks like those two, in my opinion. Rescue on a big mountain where injury is likely and folks are holed up waiting is a different story.