Algorithm for promote feature Implemented by quora?

How can I go about if I want to make the promote feature like quora? I have a user database and i am trying to choose users to promote the question to. Am considering similar interests as the criteria for promotion. I want in the algorithm that when a certain user promotes a question, it should get promoted to differnt users till all the users in the database are exhausted after which the users who have already recieved a promote request will be choosen for promotion.