I don't think it's creepy.
I've followed girls before. not like off a train ...but there have been some occasions where i've been in a shopping centre, seen a girl I like ...and walked after her. Sometimes there are too much people around to talk to her right there and then, so i maybe follow her for a minute or two and hope she goes where there are less people.
it's only creepy when she spot's you following her.
At that point I usually abort
...or just paranoid?