You earn crew members by earner Rep, doing tricks. You earn your first crew member once you have earned 1000 Rep with one Ride session. Second is earned 3k later once you get 4000, third is earned 5k later once you reach 9000 total for the session/ride.
You have to get a perk from all three of the different crew members, meaning you must have a BLUE, GREEN, AND YELLOW perk. The easiest way to notice this is if you have multiple Green perks, for example, you will only see a single crew member's face on the loading screens.
Getting 1000 points per level is about average for me, but try and pick stunt centric levels and should be able to get it in a single environment. Obviously you need to get to 9k and usually want to do that before dusk (7-8 nodes) so you'll need about 1500 a level if you start on Peaks.
You must not end the session by getting Rekt OR Retiring at the end of a level, you have to finish through the Peaks environment to finish the session. You can use the shortcut and start at Peaks, still counts!
Awaiting confirmation that it also unlocks when you click X -> End Session at the completion of any Boss Level.