Finding the right testers for your beta test is crucial, especially if you're already on the market with an existing user base. To recruit and maintain a beta testing community from your existing users, first segment your users based on demographics and in-app behavior to identify common use patterns. Then, select highly communicative users who are willing to actively participate in the beta test, as well as those showing low engagement to gain a holistic view of all users. Communicate with your user segments through personalized emails and surveys to further qualify them and set expectations for the beta test. Engage your testers with regular reports on progress and acknowledge their contributions to prevent tester burnout. Finally, nurture your community by maintaining communication throughout the testing period and between tests, and don't hesitate to remove inactive testers to maintain an active pool of beta testers.