With the significant growth in the number of start-ups the importance of addressing the issue of financing these companies has increased. Crowdfunding tools, relying on grant, debt, reward, and shareholder models, have provided suitable opportunities to meet this start-ups need. In this regard, platforms have been developed with the aim of introducing, marketing, and selecting a method of providing crowdfunding resources with the presence of investors and investors. Therefore, the purpose of this research is to design a comprehensive model for crowdfunding to support start-ups in the context of online marketing and sales platforms based on the dynamic systems analysis approach. Using the dynamic systems analysis approach, a flow chart has been introduced. Finally, by developing planning scenarios, the results of continuous event simulation and scenario evaluation have been analyzed. Given the presence of multiple influential factors in complex cause-and-effect loops, diverse feedback and causal effects, and different actors, the results indicate the effectiveness of the dynamic systems analysis approach for analyzing the problem under study. The results indicate that each of the types of financial assistance, debt, reward, and shareholder models will perform differently in a specific situation under the influence of the business scope of the start-up, the penetration rate of the crowdfunding approach, and the characteristics of the project and the decision-making environment. Therefore, choosing the appropriate model will have a significant impact on the success of campaigns designed to raise funds at the intended target level on the basis of developed online marketing and sales platforms.