Apps r gr8 but irl
Mobile apps can trigger a response, reward a behavior, allow monitoring progress.
They can do what was done in the past by people and/or pencil and paper. That's all. The awareness of the need to change, motivation to do something, and sweat and effort need to come from the teen
irl. I will post in comments apps which, at the time, seem good. Do noted that they often go through revamping, however.