This paper reports a mobile persuasive application to motivate teenagers to start and continue being physically active. Being physically active can lead to reduced risks of having weight and cardiovascular problems; however efforts in this direction had variable success. Designing technology that will be engaging and motivating for teenagers requires an understanding of the factors that contribute to behavior adoption in teenagers. To understand these, we approach the design from several theoretical models: Theory of Planned Behavior, Theory of Meaning Behavior, and Personality Theory. We found that 1) Personality traits affect perceptions on physical activities and the usefulness of devices that motivate them; 2) Favored motivational phrases are universal across traits; 3) Those who tried our prototype was generally positive and stated that they would use it on their own; 5) The characteristics of games that are desired are: social or competitive, outdoor, simple to learn and with large variations.