It sounds like something that would happen in San Francisco. In 2005, a few friends gathered for dinner and started bemoaning the fate of the planet, the environmental impact of consumer excess — and ended up challenging one another to not buy anything new for six months.

By mid-2006, the rapidly growing group was featured on the “Today” show, and people were calling it a movement.

“We think of it as more of a phenomenon than a movement,” said John Perry, a co-founder of the group, now known as the Compact. “We’re grateful for our 17 minutes of fame,” he added, “but we didn’t intend this to be broadcast. We didn’t mean to attract followers.”

Yet for such a simple and not terribly sexy idea — to buy nothing new, other than food and other absolute essentials — the Compact has managed to build a groundswell of supporters. The group has more than doubled since the fall, to nearly 8,000 members from 3,000. It has even found a footing in Europe and Australia.