Successful individuals with careers in science, technology, engineering, and math (STEM) fields, or "STEM career models," are often used to encourage students towards pursuing STEM careers. However, existing research has not yet examined whom students identify as salient STEM career models during the course of their natural schooling and how students are motivated by those models to pursue STEM careers. We surveyed a racially diverse sample of high school students (ages 14-19; N = 526) to explore "whom" students consider as STEM career models, "how" students report being motivated by those models, whether these trends differed as a function of students' gender or racial/ethnic group membership, and how different model characteristics associate with students' competence-related beliefs and interests for STEM careers. Having a STEM career model was positively associated with students' STEM career motivation. Career models were most often individuals in students' immediate social networks whom students perceived as similar. Providing socially persuasive messages, providing knowledge or advice, and modeling career behaviors were most often reported as inspiring to students. Providing knowledge or advice and modeling career behaviors were also positively associated with students' motivation. Students' racial/ethnic group membership was an important factor shaping their STEM career model experiences. Findings help to identify factors that lead high school students to perceive certain individuals as career models, thereby revealing key mechanisms through which socializers shape STEM career motivation. Implications for the development of interventions or educational programs that use career models to motivate students towards STEM careers are discussed.