Internet of Things (IoT) connects machines, devices, sensors and people. This technology is expected to connect billions of devices in the near future. Traditional methods make it very difficult to integrate and maintain so many devices. However, social networks manage to connect and maintain the communication of billions of people using social relationships. Social IoT (SIoT) is an emerging field that uses social relations to connect and maintain devices in IoT networks. This article presents a systematic literature review of conceptual papers in SIoT, together with application areas. The results show two themes from conceptual papers: Objects part of human social loop and have a role in human social network, and Objects form social network. Furthermore the results indicate that, SIoT is mostly applied in smart home environment. These findings will benefit academics and practitioners to better understand SIoT and its applications areas.