Unfortunately search and rescue is non-recreational, and therefore falls under Part 107, as the FAA has clarified a number of times. That said, as far as I'm aware the FAA has only ever pursued sUAS SAR organizations over the issue, not private individuals helping in one-off situations. So while it's not recreational flight it probably won't attract attention unless the flight caused damage or injury.
In New Mexico we (State Search and Rescue) are only permitted to use Part 107 pilots as part of the search effort, but I know that non-certified pilots do sometimes participate outside the formal SAR command structure. They certainly go out and help people look for lost pets.