I think I am stuck, is there a way to trigger a mission?

Hold the button you use to swap character Alt on PC.

Look for the number in front of Trevor, Michael and Franklin. If there is none it is because there is no mission left for that char. Swap for one who does because he is the one who will trigger that mission (the color is a hint too).

That number means the quantity of missions available for the char.

If the mission do not start when you reach the place, look for a yellow spot on the ground, or to enter some doors - I got I graphics bug with the last nvidia driver that make those disappear, as well as the circles on the stun plane. =(

Swap to Trevor and go to the apartment he is staying in

That building is (if I am correct) underneath a road. To begin the mission you need to go above the road, and the mission will be triggered. I got stuck in exactly the same way before.