Be already on the roster of your local volunteer SAR team. That's what I'm working on myself at the moment. Depending on the group, once you have the most basic training, you can be a "warm body" whenever it is convenient. Other groups are more regimented and demand a particular level of participation.

Volunteers with no credentials get upset when their help is refused, but there is a good reason. And yes, sometimes they do make the save.

There are certain basic things you need to know before you blundering around a search area leaving fresh tracks and putting scent in the air for the search dogs. Do you know that while a bloodhound will follow the trail of a specific person's scent, other types of dogs track down any human scent in the air?

Do you know that missing person searches are assumed to be crime scenes until determined otherwise, and any clues you disturb could be equivalent to tampering with evidence?