This paper addresses the problem of formation control and tracking of some reference trajectory by an Euler–Lagrange multi-agent systems. The reference trajectory is only known by a subset of agents. This work is inspired by recent results by Yang et al. and adopts an event-triggered control strategy to reduce the number of communications between agents. For that purpose, to evaluate its control input, each agent maintains estimators of the states of its neighbor agents, as well as an estimate of its reference trajectory. Communication is triggered when the discrepancy between the actual state of an agent and the estimate of this state as evaluated by neighboring agents reaches some threshold. Communications are also triggered when the reference trajectory estimate is degraded. The impact of additive state perturbations on the formation control is studied. A condition for the convergence of the multi-agent system to a stable formation is studied. The time interval between two consecutive communications by the same agent is shown to be strictly positive. Simulations show the effectiveness of the proposed approach.