You can boost your impact through social messaging or SMS, but make every text count by sending the right kind of message. A British study measured the impact of different types of motivational messages on increasing physical activity among four groups of young adults. Physical activity increased significantly more among the group that received affective texts about how exercise would make them feel (increased levels of positivity, joy, optimism, etc.), than the group that received instrumental texts about the physical benefits of exercise (heart health, weight management), the group that received both affective and instrumental messages, or the group that received no texts at all. Instead of sticking to science, it might be a good idea to highlight the emotional benefits that come with change.
Rose, T. Barker, M. Maria Jacob, C. Morrison, L. (2017). A Systematic Review of Digital Interventions for Improving the Diet and Physical Activity Behaviors of Adolescents. Journal of Adolescent Health, 61(6), 669-677.