This document proposes a framework for modeling and analyzing influence diffusion in multiplex online social networks (OSNs). It introduces coupling plans to represent how data spreads across overlapping users in multiple OSNs. Specifically, it proposes both lossless and lossy coupling plans to map multiple networks into a single network. Extensive tests on real and synthetic datasets show the coupling plans can effectively identify influential users by considering their roles across multiple OSNs. The framework provides insights into influence propagation in multiplex networks and can solve the minimum cost influence problem by exploiting algorithms for single networks.