Vehicle Ad hoc NETwork (VANET) routing is facing a lot of challenges, such as efficient and effective message forwarding in the distributed network, as well as exploring and exploiting the movement regularity among vehicles and the social ties among passengers. Oriented to the fixed-line VANET, we propose a social-based routing scheme to enable the efficient and effective message routing among passengers. In the proposed scheme, passengers are divided into different communities based on the Improved K-Clique community detection algorithm (IKC). For determining the forwarding and dropping order of messages, a Social-based Message Buffering scheme at vehicles (SMB) is devised with their closeness and contribution considered. A Bilateral Forwarder Determination method (BFD) is proposed to make the optimal message forwarding, including Intra-Community Forwarder Determination (ICFD) and intEr-Community Forwarder Determination (ECFD). Simulation results show that the proposed scheme has better message delivery ratio and lower network overhead than other existing ones.