Collectors are special characters located at the bottom of the map on certain events. They produce cards or tapes over time, but, unlike regular characters, they provide no bonus multipliers to hangouts.
Whenever ready, you can get the collector's payout by tapping the green "Collect!" balloon over it.
Despite being characters, they behave much like regular hangouts, and so their cards can be found in their own Collectors section on the hangouts screen.
You can also upgrade most collectors to increase their payout or their speed.