Most of the literature on multi-sided platforms (MSP) is descriptive and examines the mature or declining stage of the company life cycle. This thesis seeks to increase our understanding of MSP startups during the growth stage - defined to start when external funding is secured. Nineteen MSP startups that were launched and funded from 2012 to 2017 were examined against a model that is developed to interpret the mathematical formulations advanced in the literature to explain affiliations among independent suppliers, customers, and MSP operators. The results suggest that funded MSP startups affiliate with four agents: third-parties, catalysts, affiliates, and sides-on-demand to strengthen their affiliations with independent suppliers and customers. The results add knowledge to the theory of new firm growth and are relevant to founders and top management teams of MSP startups because affiliations with agents may increase their likelihood of attracting resources to grow and affect MSP startups outcomes.