In this paper, the formation control problem for a group of networked unmanned aerial vehicles (UAVs) in the presence of external disturbances has been formulated. The cooperative control for the linear multi-agent system has been generalized to the leader following formation control of multiple UAVs under fixed network topology. The exogenous signals such as reference trajectory and disturbance are produced by an exosystem which is considered as a leader in the proposed multi-agent system. The considered system topology is composed of two groups of UAVs. One group has access to the exogenous signals, while the other cannot obtain information from the exo-system. As a result of limited information exchange, this problem cannot be solved by centralized control approach. This paper discusses the formulation of the distributive observer for the formation control of UAVs as an application of the co-operative control problem. UAVs maintain their formation geometry by keeping a relative distance to the leader UAV and track a predefined trajectory during their flight through a dynamic distributive output control law. Working of the proposed control approach and its effectiveness is presented through simulation results.