The research substantiates the scientific and applied approaches to the selection of crowdfunding platforms for financing innovative projects in the context of the development of the institutional structure of the start-up market. The analysis of the main tendencies of the development of tools and mechanisms of crowdfunding, as well as the existing theoretical and methodical approaches to the choice of instruments and mechanisms of the operation of crowdfunding, is carried out. It is established that by choosing between the variety of existing crowdfunding platforms, the following factors need to be taken into account: the essence of the innovation project, the stage of development of the project, the direction of the projects, the mechanism for the remuneration of the investor, the mechanism of accumulation and disposal of the accumulated amount of cash. A comparative analysis of 24 largest crowdfunding platforms functioning allowed to identify and classify the common features and differences in the activities of these platforms, to differentiate them according to the stages of start-ups development, by treating a plurality of platforms in three key groups (A, B and C), which differ in stages of development of startups, which can use this platform, and the platform use mechanism. It is proved that the choice of the crowdfunding platform should be realized based on the crowdfunding model characteristic for the given platform, the type of financing and the possible financial expenses associated with using the platform. The structural-logical mechanism for choosing of the crowdfunding platform in financing innovative projects is scientifically substantiated, which implies expansion of the range of financial instruments, the emergence of additional institutional obligations between the entrepreneur and the investor and support by operational rules. Practically, this mechanism allows to make a reasonable choice of the platform, based on its own institutional and operational requirements and representations about the further development of the project. Directions for further research include the distribution of risks using the mechanism of crowdfunding, distribution of responsibility and financial flows between the participants of the social investment agreements.