We study in this paper crowdfunding from the platform perspective. We consider a platform where several project campaigns are running and competing on fund collection. The platform manager's objective is to increase the proportion of successful projects and he uses the lever of project promotion on the platform website to influence the funders' and balance the potential future funds between projects. We first consider the platform policy derivation as an optimization problem and show to derive the optimal project promotion policy. We then consider the more realistic setting where the platform manager adapts his policy online when observing the status of fund collection. We model this online strategy as a real option and develop a dynamic programming algorithm that finds the optimal strategy depending on the observed project campaign status.