Followers are a resource that you can gather which add to your overall House Points!
They start appearing further in the city map, and you can collect them from Activities in the City such as the Basketball Courts or Dance Floor sites. Beware however as Followers can be stolen from you if another player causes Drama with you (PVP)! This means you can loot them from other players too!
How do I check how many Followers I have?
Tap on Phone at the bottom right hand of your screen. Go to the Trending page. Tap on the little 'i' icon next to Trending, and there you'll see a breakdown of your House Points into Followers and Influence!
According to this screenshot, this user has 858, 869 Followers! Phew, they're famous.