Thompson, who had basic first aid training, took care of the wounded as the team helped stunned survivors to begin clearing the chaos.
"People were lethargic to clean up, doing a little bit kept people motivated," one of them said.
Week by week they dug toilets, collected corpses, played with children, built shelters, found food, got the school going, and tried to restore morale.
By the third week, the volunteers numbered 10 as other westerners signed on.
By week seven they were 40, including voluntary doctors.
The group was never financed, getting help from time to time from organised aid associations, who donated medicine or food, or from passers-by who left what cash they could.
"It was giving hope and reintroducing normalcy", said one volunteer in the film.
By the time the group left after several months, 520 homes had been rebuilt with no organised outside financial help.
Penn saw the film on the behest of Czech model Petra Nemcova, who was in Thailand on holidays when