In vehicular networks (VNs), due to the high deployment cost of infrastructure, namely road side unit (RSU), RSUs can be deployed sparsely. The sparse RSU placement, coupled with the RSUs' limited coverage range, has led to the existence of uncovered areas between two consecutive RSUs. When vehicles transition within these areas, the problem is that they must frequently experience service disruptions. This paper proposes a cooperation scheme that combines vehicle-to-vehicle (V2V) communication with the existing vehicle-to-infrastructure (V2I) communication to address the above problem. Specifically, a multi-hop forwarding scheme among vehicles is proposed. When a target vehicle has just left a RSU's coverage range, it searches the farthest forwarder from its neighboring vehicles behind it. If the forwarder also enters the uncovered area, it will generate a multi-hop path back to that RSU's coverage range using the same strategy of the target vehicle. Thus, there is always a multi-hop forwarding path to the target vehicle through V2V communications in the uncovered area. The analytical expressions are derived for the average achieved throughput and the average number of service disruption times at the target vehicle. Through a close agreement between analytical and simulation results, the advantages of our proposed scheme, such as high average throughput and service continuity, are verified. Additionally, the results indicate the improvement of our scheme compared to the sole V2I network.