A Mobile Ad Hoc Network (MANET) is becoming a practical platform for pervasive social networking. For example, people chat with each other via MANET for instant social activities. How to help mobile users build up trust in pervasive social chatting is becoming an important and interesting issue. By applying a method for usable trust management, we designed PerChatRep, a reputation system for pervasive social chatting based on the result of a need assessment survey. We evaluated the effectiveness and robustness of PerChatRep through simulations. Furthermore, we implemented the system by applying Nokia N900 smart phones as MANET nodes based on a distributed energy-efficient social networking platform. We further conducted a two-session controlled user experiment to investigate the impacts of PerChatRep on mobile users. Results show the usefulness and user acceptance of PerChatRep. (C) 2012 Elsevier Inc. All rights reserved.