Device-to-Device (D2D) communication is a promising solution in next generation cellular technologies to efficiently provide on-demand connectivity. Among existing D2D communication schemes, the outband approach that uses unlicensed spectrum can eliminate the spectrum interference with cellular links. Although the autonomous outband is a strong option because of its simple operation, it is a significant problem to appropriately encourage the participation of mobile users. To address this issue, this paper proposes a gamified participatory D2D (GP-D2D) communication where mobile users compete their gain that is obtained through providing network connectivity for other mobile users. The contribution of this work is to propose a novel approach of the autonomous outband D2D communication for efficiently encouraging the active participation of mobile users. The feasibility of the proposed gamified approach is confirmed with theoretical analysis and computer simulations. It is implied from the results that gamification is an effective approach for autonomous D2D communication by defining appropriate game-settings such as gain mechanisms.