Community activist groups typically rely on core groups of highly motivated members. In this paper we consider how crowdsourcing strategies can be used to supplement the activities of pro-environmental community activists, thus increasing the scalability of their campaigns. We focus on mobile data collection applications and strategies that can be used to engage casual participants in pro-environmental data collection. We report the results of a study that used both quantitative and qualitative methods to investigate the impact of different motivational factors and strategies, including both intrinsic and extrinsic motivators. The study compared and provides empirical evidence for the effectiveness of two extrinsic motivation strategies, pointification - a subset of gamification - and financial incentives. Prior environmental interest is also assessed as an intrinsic motivation factor. In contrast to previous HCI research on pro-environmental technology, much of which has focused on individual behavior change, this paper offers new insights and recommendations on the design of systems that target groups and communities.