We conducted proteomic profiling of plasma, identifying both overlapping and unique differential proteins in adolescent patients diagnosed with major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ). Our results showed that the protein signatures of adolescent psychiatric disorders differ significantly from those of adults. We propose potential targets for drug development aimed at the prevention or precision therapy of these psychiatric disorders. These findings enhance our understanding of the molecular etiology of adolescent psychiatric disorders. The specific biomolecular signatures of MDD, BD, and SZ could potentially serve as targets for the development of novel interventions aimed at prevention, early diagnosis, and treatment of these mental health conditions.