Here's an example that shows coordinates at start and end, with . . . while in touch.
One thing to check is that you have Use mouse input set to Yes if you are using touch on a computer where you have a mouse rather than touch device. Forget to do this and it will seem like on touch start isn't working, mostly because...it isn't!
PS. One other thing you should check is the type of variable you are using. In this example I used global variables. But if you are using a local variable, it could be you have a "scope" problem. Local variables are only visible inside the construct where they are created. So if you create a local variable inside a loop, it is only available inside that loop, and it gets reset back to its initial value (default 0) each time the loop starts.