This paper considers a two-echelon supply chain in which demand is jointly influenced by network externalities, advertising, and price. The purpose is to investigate the impacts of network externalities on the pricing and advertising decisions of supply chain members, as well as on contract selection. The results show that network externalities increase product prices and advertising investments, which creates a double superposition advertising effect that significantly increases sales and benefits both the retailer and the manufacturer. However, double marginalization still exists in the decentralized system, meaning that product sales, advertising investment and system profit are all better under the centralized system. The advertising cooperative contract and revenue-sharing contract are examined to coordinate the supply chain. It is found that only the revenue-sharing contract can successfully coordinate the supply chain when the strength of network externalities is weak, under some conditions. When network externalities are strong, both contracts can coordinate the supply chain, but the revenue-sharing contract is more efficient.