We consider the collective dynamics for a multi-agent system with a virtual leader. The velocity of the leader is time-varying and the interconnection topology of position network is switching based on the distances between agents. To track the leader in flocking, a neighbour-based local piecewise smooth controller is proposed for each agent. Using the control method, all agent velocities asymptotically approach the desired velocity while collisions can be avoided between agents. Some simulation results are provided to demonstrate the theoretical results.