Background: Teens and young adults in the United States are in need of sexual and reproductive health information, as evidenced by elevated rates of sexually transmitted infections (STIs), pregnancy, and births among this population. In-person sexuality education programs are helpful, but they are unlikely to rapidly accommodate teens and young adults in a moment of crisis. Evidence suggests that technologies such as instant messaging (IM) and text messaging may be effective ways to provide teens and young adults with sexual and reproductive health information. In September 2010, Planned Parenthood Federation of America launched a text and IM program designed to provide immediate answers to urgent sexual and reproductive health questions from a reliable and confidential source and to link young people to sexual and reproductive health services if needed. Objective: To assess whether this program is successful in reaching the target population, whether user characteristics vary by mode (IM vs text), and whether mode is associated with reaching individuals with high levels of worry or reducing worry postchat. Methods: Data were collected from prechat and postchat surveys for all IM and text message conversations between September 2010 and August 2011. A bivariate analysis was conducted using chi-square tests for differences in the main covariates by mode of conversation. In the multivariable analysis, logistic regression was used to identify factors that were independently associated with prechat levels of worry and changes in worry postchat. Results: A total of 32,589 conversations occurred during the program's first year. The odds of feeling very worried prechat were highest for IM users (adjusted odds ratio [AOR] 1.43, 95% CI 1.20-1.72), users 17 years and younger (AOR 1.62, 95% CI 1.50-1.74), Latino/Hispanic users (AOR 1.36, 95% CI 1.27-1.46), and black users (AOR 1.40, 95% CI 1.30-1.50). After controlling for the study covariates, there was no significant difference in the odds of feeling better (less worried) postchat between IM and text message users. Feeling better postchat was associated with being younger (<= 17 years: AOR 1.42, 95% CI 1.17-1.72; 18-24 years: AOR 1.20, 95% CI 1.02-1.42), being Latino/Hispanic (AOR 1.31, 95% CI 1.10-1.55), reporting that the service was very helpful (AOR 3.47, 95% CI 3.24-4.32), and asking about emergency contraception (AOR 1.35, 95% CI 1.13-1.61). The odds of feeling better were lowest for users with questions about STIs (AOR 0.61, 95% CI 0.47-0.78). Conclusions: The results from the process evaluation suggest that the program was able to provide informational support to vulnerable groups, such as teens and racial minorities, in moments of particular worry. Differences between the IM and text message users reveal that each mode appeals to a different population and that both are necessary to reach a diverse audience.