A part of the logic to simulate movement is as simple as randomly adding movements to the Latitude/Longitude. So, use a Timer that triggers every second or so and subscribe to that "Timer" event, where you write the code that moves the car.
If you have a property on the Car that you can call "location" of baseType LOCATION with, then it must be set as "logged" on your simulator code for you to update the location property with the new location (in case of any movement since its last location). Also, do set the car Thing's ValueStream property to store the changes in location.
Trying using ThingWorx Marketplace Google Maps extension for showing Location and Paths on Google Maps from the recorded simulation by Setting a location property in Thingworx like this:
me.location = { latittude: latitude_value, longitude: longitude_value, elevation: elevation_value, units: "WGS84" }