Target Users for Growth Launch

Scenario

You are the PM for a large knowledge-sharing platform with a mature reader base, a smaller but highly valuable contributor base, and multiple growth surfaces across feed, notifications, email, onboarding, and answer creation. Leadership wants to fund a new growth initiative, but past launches that targeted everyone at once produced weak results because user intent varies widely across new readers, occasional readers, active answerers, and topic followers. The platform has 50M monthly active users, but only 28% of new signups are retained after 8 weeks, while users who follow 5 or more topics and read 3 or more answers in their first week retain at more than 2x the baseline. You need to decide which users to target first so the initiative has the highest chance of creating durable growth rather than a short-term spike.

Question

How would you decide which users to target first for this growth initiative, and how would you determine whether your initial segment choice is the right one before expanding further?