Online and mobile crowdsourcing services call for thorough definition of components and attributes. As cloud-based services have become widely adopted, a cloudified reference model has been emergent for crowdsourcing platforms and applications. This paper, introduces for the first time a cloudified four-phase reference model for crowdsourcing along with a generic workflow for crowdsourcing development utilizing the facilities offered by cloud service providers. Moreover, useful insights are presented for the evolution of today's online crowdsourcing applications and platforms towards the concept of crowdsourcing as a service.