To accelerate the development of mobile apps, more and more third-party services that can be consumed as mobile backend services are available for the consumption of mobile developers. However, with the growth of mobile backend services, it turns to be a more and more challenging process for mobile developers to discover mobile backend services with high return-on-investment (ROI). Due to the unique characteristics of mobile backend services, directly applying existing Web service recommendation solutions for mobile backend services is ineffective. In this paper, we systematically studied and summarized four unique characteristics of mobile backend services. Based on these four unique characteristics, we proposed an extendable recommendation approach for mobile backend services to help mobile developers to efficiently identify what they really need. Through the empirical evaluations that we conducted on hundreds of open mobile backend services, we demonstrated the effectiveness and efficiency of the proposed approach.