We propose and investigate cooperative visible light communications (VLC) enabled vehicular network architecture with an unmanned aerial vehicle (UAV) relay. In the proposed system, a UAV equipped with an onboard photodetector and light-emitting diodes is used as a relay in a vehicular VLC link. The advantage of having a flying UAV relay is its great mobility and ease of deployment. The performance of UAV-assisted cooperative VLC is investigated for amplify and forward and decode and forward protocols with half duplex and full duplex modes. Moreover, location of the UAV relay is optimized in order to maximize the signal-to-noise ratio at the destination vehicle. The active light beam tracking technique is further employed to increase the reliability of the proposed VLC system. Our results reveal that a UAV relay can significantly improve the transmission performance of conventional VLC-based vehicular networks.