The one who is being crept upon.
Pronounced similarly to 'creepy,' but with a more drawn out 'e' on the end.
Because most un-adored creepers don't actually talk to people, the creepee is usually only ever spoken of between an affectionate creeper/creepee
Girl: Aww, Matt, you're my creeper. I love you.
Matt: Aww, random girl, you're my creepee. I love you too.