This paper presents an online dynamic path planning approach for multiple UAVs tasked with monitoring ground convoys. Specifically, the UAVs are considered to fly in an elliptical formation around the convoy at a given height, whose formation parameters are to be optimized. A metric is designed to measure the surveillance quality of the UAVs which is computed as their cumulative surveillance area around the moving convoy in a specified time window. Then, an optimization problem is formulated and solved online to maximize the surveillance quality metric, thus obtaining the formation parameters and the assigned positions of the UAVs in the formation. Simulation results showcase the approach’s effectiveness and real-time capability, providing superior surveillance compared to static strategies.