i am not a lawyer, but to the best of my knowledge there are specific criteria for "stalking", one of which being that the stalking causes fear or distress.

the average person (i.e. a "reasonable person" by legal definition, even if us tech folk don't consider it reasonable) is not particularly scared or distressed by targeted ads. some people even like them.

a good lawyer might be able to make something out of it, but i'm not convinced that stalking laws are the right avenue.