Table 3.

Summary of activities on the private Slack group.

Week	Design activity	Purpose and activities	Clinician completion rate (n=10), n (%)	Teen completion rate (n=8), n (%)
1	Introductions	Learning how to use features of Slack Getting to know other participants	10 (100)	7 (88)
2	Technology to manage mood	Sharing current strategies and technologies that participants have found helpful for their clients (clinicians) and themselves (teens and clinicians)	10 (100)	7 (88)
3	Internet-based mental health support, part 1	Learning about more features of Slack such as polls with example poll Ideating on benefits and challenges of using the internet-based platform of Slack	10 (100)	7 (88)
4	Internet-based mental health support, part 2	Voting polls on preferred features of Slack for internet-based support with mood Voting polls for the format of the internet-based support (eg, group vs individual) and the length of internet-based support	9 (90)	8 (100)
5	Adapting BAa to the web	Psychoeducational video explaining BA Prototype: obtain feedback on a summary of BA activities for 6-week format (Multimedia Appendix 4)	9 (90)	7 (88)
6	BA Model and activity monitoring	Explaining BA model with a video and concepts through slides (Figure 2) and ask participants to give examples from their lives by uploading hand-drawings (Figure 3) Prototype: mock-up of mood and activity monitoring in survey format	8 (80)	6 (75)
7	Upward and downward spiraling of mood; introducing SMARTb goals	Providing feedback on upward and downward spiraling of mood and planning SMART goals Prototypes: Survey format for reflecting on upward and downward spirals in mood and action (Figure 4) Survey format for individually planning a SMART goal, mini-steps, and setting reminders	8 (80)	6 (75)
8	SMART goal planning	Providing feedback on technological adaptations of planning a SMART goal, mini-steps, and setting reminders Prototypes: Mock-up of chatbot format Direct messaging format in which participants pair up with a peer and a researcher moderator. Participants were asked to share SMART goals and provide feedback on each other’s goals	7 (70)	6 (75)
9	Overcoming barriers	Providing feedback on overcoming barriers to mini-steps and SMART goals. Prototypes: Survey format Chatbot format with prompts to overcome barriers (Figure 5) Direct messaging format by pairing up with a peer from week 8, following up, and sharing barriers	7 (70)	4 (50)
10	Teaching components	Identifying how to deliver teaching components of BA in internet-based formats such as videos and chatbots	7 (70)	4 (50)
11-12	Exit interviews and surveys	Providing feedback on the method and follow-up questions on depression management	9 (90)	5 (63)

^aBA: behavioral activation.

^bSMART: specific, measurable, appealing, realistic, and timebound.