Group members then became angry at claims that the new administrators wanted them to pay to promote their local businesses to each other.
Facebook does not specifically state that "admins" cannot sell their rights but the role is usually voluntary.
Local groups exist for communities to share news and events.
The group for Facebook members living in Northfields, west London, had more than 25,000 members.
Thousands have left, and many of those remaining are taking on administrator roles themselves in order to reclaim the group.
They have renamed it "Northfields People Please Leave This Group" and are telling members to join an alternative page.
Kathryn Coles established the Northfields Friends group in 2011 but was no longer running it at the time of the sale.
"A lot of people are really angry - on a number of levels," she said.
"People say London doesn't have communities but it does. A lot of people have real affection for the group