Sexually transmitted infections (STIs) are caused by fungi, bacteria, parasites or viruses and are transmitted from one person to another through having intercourse. Lack of knowledge will cause teenagers to have sex unsafely. Teenagers need to be taught about reproductive health because STIs are common and there is little knowledge about STIs. This study aimed to find out the effectiveness of a virtual peer educator training program about STIs in teenagers. This was a quantitative quasiexperimental study. There were 38 participants who were aged 15-18 years old and were recruited through convenience sampling. The data were collected by using two questionnaires: one about the awareness of STIs (Cronbach’s alpha = 0.795) and one about the attitudes towards STIs (Cronbach’s alpha = 0.709). The data were analyzed by using paired t-tests. This study showed that the training program was effective in enhancing teenagers’ awareness and attitude about STIs. Educating teenagers about reproductive health is important to make they know about STIs, themselves and their surroundings. Keywords: virtual, peer educator, training, STI, youth