This is a randomized (drug assigned by chance), double-blind (a medical research study in which neither the researchers nor the participants know what treatment the participant is receiving), placebo-controlled, parallel (a medical research study comparing the response in two or more groups of participants receiving different treatments), multicenter of ustekinumab in adolescent participants with moderate to severe psoriasis. The total duration of study will be 60 weeks. The study will consists of 2 parts; a Screening period and a Treatment period. In treatment period participants will receive either ustekinumab half standard dosage, ustekinumab standard dosage or Placebo. Participants receiving ustekinumab half standard dosage and ustekinumab standard dosage at Week 0, will receive placebo at Week 12 and participants receiving placebo at Week 0 will be randomly assigned to either ustekinumab half standard dosage or ustekinumab standard dosage Weeks 12, 16, 28, and 40. Primarily efficacy will be evaluated by physician's global assessment (PGA) score of cleared or minimal disease. Participants' safety will be monitored throughout the study.