Online marketplaces confront the challenge of the "Penguin Problem," i.e. how to attract their first users and leverage network effects. Susan Spender puzzles over how to get started with her platform business connecting pet owners to pet enthusiasts who perform small tasks, such as feeding and dog walking. She and her team explore four popular platform companies - Eventbrite, GrubHub, Instacart, and TaskRabbit - and learn from their startup strategies. By comparing and contrasting the four companies, students explore a series of possible approaches for tackling this crucial issue of platform entrepreneurship and differentiate which strategy works for which company/industry. The "Platform Business Model Canvas" helps them identify the key elements of platform entrepreneurship and see how they are interrelated.