Communicating the risks associated with nicotine and tobacco use to adolescents can be challenging, especially with the current tobacco market's attempt to capture the attention of youths. Text message interventions have emerged to address the need to improve tobacco risk communication. This article informs the design of a message library for tobacco risk communication that is based on the transtheoretical model and addresses the risk of multiple tobacco products. We draw findings from this study from two phases. Phase 1 involved six remote focus group discussions (n = 25) and an in-depth interview, and Phase 2 involved online ideation sessions (n = 11) that led to the current version of the messages. We conducted the study within a larger project for the design and testing of a tobacco prevention program. With thematic analysis and the affinity mapping technique, two research team members identified repeated topics and relevant quotes to organize them into themes and subthemes. In Phase 1, thematic analysis revealed four major themes: 1) Adolescents' gap in tobacco knowledge, 2) Social influence and popularity, 3) Attitude toward marketing, and 4) Text message framing preferences. During Phase 2, participants generated 1-to-7 iterations of the original messages. Votings and discussions resulted in a library of 306 messages under 7 sections, categorized based on the processes of change from the transtheoretical model. The current study presents key insights crucial for developing and evaluating a library of tobacco prevention text messages that is scientifically valid and successfully resonates with today's adolescents. Our future plan is to go beyond this initial message development and vet the message library by adolescents and expert reviewers in tobacco risk communication. Future research may consider developing messages that are tailored based on gender, ethnicity, and other factors that are predictive of tobacco use.