The rapid development of mobile internet technology and the better availability of GPS have made mobile online social networks (mOSNs) more popular than traditional online social networks (OSNs) over the last few years. They necessitate fundamental social operations such as establishing friend relationship, location sharing among friends, and providing location-based services. As a consequence, security and privacy issues demands the utmost importance to mOSNs users. The first stream of existing solutions adopts two different servers to store locations-based and social network-based information separately, thereby sustaining large storage and communication overhead. The second stream of solutions aims at integrating the social network server and the location-based server into a single entity. However, as these approaches exploit only one single server, they may face several performance issues related to server bottlenecks. Moreover, such schemes are found to be vulnerable to various active and passive security attacks. In this paper, we propose a privacy preserving, secure and efficient location sharing scheme for mOSNs, which shows both efficiency and flexibility in the location update, sharing, and query of social friends and social strangers. The security of the proposed scheme is validated using random oracle based formal security proof and Burrows-Abadi-Needham (BAN) logic based authentication proof, followed by informal security analysis. Additionally, we have used ProVerif 1.93 to verify the security of the system. The efficiency and practicability of the proposed scheme are demonstrated through experimental implementation and evaluation.