In OK City, go up to the ramp that you put in place with the fork-lift and into the secret garage. Grind on the black box, and it will open up into a vert vamp. Use the ramp to grind onto the bullhorns, and jump into the small room to unlock Day Smith.
In L.A. on top of the brick building you will see a girl sitting down. Do an adrenaline trick in front of her that equals 20,000+ points to unlock Vanessa. You can manual in between tricks, as you don't have to do a 20,000 point single trick.
Successfully complete the game by completing all objectives with any rider to unlock Volcano.
