Vulnerable populations facing stigmatized conditions often fail to seek help despite high need. Social campaigns aim to address this gap by combining elements like awareness-raising, peer-to-peer dissemination, and calls for action, yet how these components interact—and potentially conflict–remains poorly understood. We develop a formal model quantifying tradeoffs between message reach, viral spread, and behavioral conversion, and then test it experimentally by promoting mental health care among Ukrainian refugees in Germany (N=1,993). While simple messages spread more readily, relatable patient testimonials proved 85% more effective at converting high-need individuals to action than celebrity endorsements (7.8 vs 4.2 conversions per 100 seeds). Explicit encouragement to share backfired, reducing uptake. These findings reveal fundamental tensions in designing campaigns for stigmatized behaviors: messages optimized for viral spread may fail to motivate action among those most in need. (Joint work with Alexandra Avdeenko, Luc Behaghel, Esther Duflo, Andreas Ette, Yagan Hazard, Alexander Moldavski, Nicolas Rüsch, and C. Katharina Spiess.)
