Facebook on Monday announced Marketplace, a new mobile app that facilitates buying and selling between peers. Marketplace allows members of a community to discover, buy and sell items, noted Facebook Product Management Director Mary Ku. The service is scheduled for rollout this week in the United States, UK, Australia and New Zealand. Users can access Marketplace by tapping a shopping icon at the bottom of the Facebook mobile app. The opening screen displays photos of items for sale by people who live in a user-defined geographic area.