Vehicular ad hoc networks (VANETs) provide an effective technology for vehicles communicating while on the road. Vehicles are organized in an ad hoc networks offering support for both safety-critical messaging, multi-hop entertainment applications, and connection to internet services through Road Side Units (RSUs). Sharing data between connected vehicles can help commuting people exchange travel information, and allows content delivery and entertainment applications using Peer-to-Peer (P2P) techniques. Despite the widely documented benefits of P2P techniques, there are a number of challenges faced when deployed in such a highly dynamic environments as VANETs. Such difficulties include the broadcast storm problem, network partition, and the temporal network fragmentation to name few. These issues are principally due to the high mobility of vehicles and thus to the constantly changing topology of the network. In this paper, we present a survey of the existing P2P approaches in the context of VANETs including a comprehensive survey of the various problems related to data sharing in VANET using P2P techniques, along with their proposed solutions from the perspective of data access, information lookup, routing, and message management. In this study, we provide a classification of the studied approaches in terms of network overlays, information structures, and network coding. To differentiate between the discussed approaches, we include a comparative study based on the crucial parameters and identify and discuss the open research challenges in P2P techniques. To the best of our knowledge, this survey constitutes the first attempt at a comprehensive analysis of P2P approaches in VANETs, which describes more appropriately the state-of-art of this specific topic of research.