Testing strategy for a real time multi user mobile app

I am testing an Android mobile app that allows multiple users to vote on the question in real-time and aggregated response/feedback is displayed immediately. I can test this app with a couple of handsets I have to verify if multiple users are able to vote in real-time. However, to test if a large number of users will be supported without issue in the app, this method is not practical. I am not sure if there is any testing framework through which I can simulate a large number of users to test this behavior at scale. Any pointers are really appreciated! Thanks!