The COVID-19 vaccine is widely available to adolescents in the U.S.; however, vaccine hesitancy poses a threat to full coverage. The literature shows that perceived risks and the presence or lack of motivators are determinants for vaccination decisions, yet research evidence from minors is scant. This study adopted the Protection Motivation framework to identify differences in these facilitators and compare the influence of internal and external motivators among American adolescents in COVID-19 vaccine uptake. A nationwide online survey analyzed 13–17-year-old teenagers’ COVID-19 beliefs as well as present or potential reasons for accepting the vaccine. Of the 439 participants, 21.18% were not and did not plan to get vaccinated. Another 52.39% had at least one dosage, of which over three-quarters were internally motivated (whereas those unvaccinated were more likely to be externally motivated, X2 = 4.117, p = 0.042). In unvaccinated individuals, older adolescents reported slightly more internal motivators than younger adolescents (t = −2.023, p = 0.046). Internal motivation was associated with higher risk perception (r2 = 0.06651, p = 0.001), but risk perception had a stronger relationship with vaccination status (r2 = 0.1816, p < 0.001), with vaccinated individuals showing higher risk perception than those unvaccinated (mean difference = 0.42 on a scale of 1–4; t = −3.603, p < 0.001); the risk perception difference was even greater between hesitant and non-hesitant participants (mean difference = 0.63; t = −0.892, p < 0.001). The relationship was moderated by perceived knowledge, where the difference in risk perception between vaccination status was only significant for those with low perceived knowledge (f = 10.59, p = 0.001). Increasing awareness of disease risks and stressing internal motivators may be key to improving uptake in young people. Future research could delve deeper into risk perception formation of adolescents and why and how it differs across populations.