Most work on social interactions studies a single, composite effect of interactions within a group. Yet in the case of sexual initiation, there are two distinct social mechanisms—peer‐group norms and partner availability—with separate effects and different potential interventions. Here I develop an equilibrium search and matching model for first sexual partners that specifies distinct roles for these two mechanisms as part of demand and supply. I estimate the model using a national sample of high school students, with data over time on individual virginity status. The results indicate that peer‐group norms have a large effect on the timing of sexual initiation for both boys and girls. Changes in opposite‐gender search behavior (i.e., partner availability) also have a large impact on initiation rates for boys, but not for girls.

Social interaction models mechanisms sexual activity youth structural estimation C31 C33 J13