system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do popular social media apps become popular when they start out with 0 users?

Take snapchat for example, you would think people would only use it when a sizable portion of their friends are using it too which explains why it is popular now, but how do people launch such things that are compelling for people to be the first people to "use" them before they spread?
gpt
usually an app will be tested by a group of people who the app is targeted at and the developers will see how they use it and then try to  cater it towards that market of users. once they know exactly what people want from the app/social media its entirely about marketing. getting the word out there, tell your friends about the app, they tell their friends, the userbase grows.