Facebook, the leading social networking site, has opened its platform to developers and allow them to publishapplications. Subsequently, numerous Facebook applications of various types were designed and deployed.Despite a huge portion of applications without business context, there exist a substantially increasing number ofapplications tailored specifically for marketing and advertising. From a business perspective, a Facebookapplication possesses the advantages of low development costs and strong word-of-mouth effect, which providean ideal alternative to traditional advertising formats. This paper utilizes the well-known Bass model forforecasting product diffusion, and proposes its adaptation to produce an optimal promotion budget allocation forFacebook applications. For a given application promotional budget to be used over a fixed timeframe, the modeloffers a unique solution for allocating the funds between direct promotion and indirect promotion(word-of-mouth) in order to achieve a maximum percentage of user installations from the target population ofpotential users. Numerical examples are provided to illustrate the optimal solution and suggestions are made forfuture research necessary to validate the model for possible use by practitioners.