Police officers are privileged with a lot of private information about the people they ticket, such as their home address or phone number. That information is confidential and should not be used by the officer in any manner other than what their job dictates. This cop taking that information, and using it for his own private motives of tracking her down and asking her out is not only creepy and stalkerish, but it's also a breach of confidentiality.
Now if the girl had tracked him down, she's not obligated under any confidentiality agreement. She would just be seeking him out under her own free will, and I think that would be considered okay. What's not okay is the officer forcing her, by law, to provide her home information, and then him using that information for his own stalkery purposes.