In the last decades, mental health disorders have been a growing source of the global burden of disease. Thousands of mental health apps are available nowadays addressing this problem, but studies show that the effectiveness of these apps is jeopardized by the low user engagement.This study investigates the most potentially effective gamification and nudging techniques in design for improving engagement in mental health apps for young people, by carrying out app-reviews for top installed mental health apps on Google play store and connecting it with engagement data, in addition to conducting expert-interviews with professionals from gamification and design background.From the findings, techniques that participated in improving retention rates included using app character for creating app narrative and user interaction, in addition to adopting a non-forcible language. While to improve app daily duration of use, simplification nudge, and stating the recommended minutes of use found to be useful. Personalization and social interaction techniques were potentially effective for improving the frequency of app daily use. For the young age group, using juicy feedback and high-quality gamification were recommended