Introduction: Adolescents aged 10–19 years account for a growing proportion of people living with HIV (PLHIV). In 2023, 140,000 adolescents were diagnosed with HIV, yet knowledge of HIV status and uptake of testing services remain critically low. Index testing—offering testing to contacts of PLHIV—is an important case-finding strategy. In 2021, President's Emergency Plan for AIDS Relief expanded guidance to explicitly include older adolescents aged 15–19 years. We reviewed index testing data to assess uptake and case-finding trends among biological adolescent-aged children and siblings of PLHIV aged 10–19 years. Methods: Routinely collected programmatic data from 27 U.S. Agency for International Development-supported President's Emergency Plan for AIDS Relief country and regional programs were analyzed for fiscal years (FY) 2017 through FY2022 (October 2016–September 2022). We compared the volume of index testing and subsequent new diagnoses across FYs and countries among biological adolescent-aged children and siblings of PLHIV and disaggregated by age, 10–14 and 15–19 years, and sex. Results: Index testing among adolescents aged 10–19 years increased from FY17 to FY22, nearly doubling from 147,088 to 291,534. Similarly, new diagnoses among adolescents increased between FY17 and FY22 (3721 vs 10,730). Overall, across FYs, index testing uptake and case-finding were higher among females than males, and the gap in testing uptake between sexes was larger for older than younger adolescents. Conclusions: Index testing uptake has increased substantially among adolescents over time, with rebounded gains for adolescents aged 15–19 years noted beginning in FY21. However, uptake across age and sex remained uneven, highlighting an opportunity to ensure that targeted testing strategies are used to reach adolescents aged 15–19 years and males.