I understood, Thank you Aya

It depends who they're talking to. If they say it to you, they're saying "You're like a stalker." If they point at someone else and say the phrase, they're referring to them acting like a stalker. In Japanese we don't really use the word "you" when we're talking to someone. :)

Thank you very much Georgia and rjcorraya

Yes, it does mean "(He/She is) like a stalker". So, you can use this to someone whom you are thinking as a stalker and is stalking someone. Obviously, this is an informal language so don't go on using it on someone who doesn't deserve to hear this phrase!!! Haha! Hope my answer helped also (^_^)

I believe this means either: You/they/he/she look like/act like/seem like a stalker.