As the mobile technology advances, various mobile peer-to-peer (P2P) systems have been developed. Since mobile devices have limited energy capacity, efficient use of the energy is indispensable for mobile P2P systems. In this paper, we propose an energy-efficient P2P system that is a type of the double-layered P2P systems in which files are searched mainly through the peers in the upper level, called super peers. The proposed system selects greedily the peers with more energy as super peers. The peers in the proposed system can identify themselves as super peers or sub-peers autonomously in a decentralized manner. We also propose three energy-efficient routing schemes, each of which is incorporated with the proposed system individually. The first routing scheme tries to utilize the energy of the peers on the routes more evenly, the second scheme chooses a route with the 'strongest' peer among the peers each of which is the 'weakest' peer on a route, and the last scheme selects a route with the second scheme among the routes with the smallest number of hops. Note that a routing scheme is applied each time when a route between a pair of super peers is chosen during the message transmission. Functionality and performances were evaluated through various experiments, and the results showed that the proposed P2P system with the third routing scheme improved theaverage network lifetimes by 368% and 22% over the doublelayered and the proposed systems without applying any proposed scheme, respectively.