I dont think you can track someone via phone number.(maybe i am wrong)
But it is easier via facebook,especialy if the user is a little bit idiot and dont protect himself.You can see where he usually go (coffee,restaurant,school etc). You can learn his habbits.Or track on of his friends, and by phishing him,you can learn more info about your target.I have done it some times, you cant believe how idiot some people are.