Setting boundaries in the workplace

There's this guy I had accidentally mistaken for someone I knew once who turned out to be a new person at work. My place of employment cycles through new people frequently that it isn't that surprising to run into unfamiliar faces every now and then. He seems very shy and awkward. Since that incident, he has initiated one conversation with me when he happened to catch me by myself during a break. Since then, he stares at me frequently or greets me as if there is an established familiarity.

I don't think he's a bad guy and much of my discomfort stems from not knowing him well (I honestly don't have any desire to get to know him, I generally keep to myself at work and a few close acquaintances). I understand that from his point of view, I am well liked and respected, I express my opinions openly and only those who know me very well understand that I generally keep to myself. He could just be trying to make friends but just combined with the constant staring, and seeking me out when I have deliberately made a lot of effort to avoid him and discourage any kind of contact is frustrating. I've sent him nonverbal cues such as not smiling or deliberately not making any eye contact when I happen to run into him that I'm at a point where I would like to actually say something but I'm not quite sure how to word it.

I feel like this person is infringing on my personal space and I'm not sure how to communicate that without making him upset or to make him stop the behavior he has been exhibiting (looking at me constantly, trying to make small talk at the most awkward moments like when I'm busy or trying to concentrate on a task) because whenever he makes his presence known it's just annoying to me.

I understand that it's not easy being a new person at any place but he's also free to befriend other people than myself. There are a lot of folks that are very friendly with him that I'm hoping at some point he would get tired of pursuing an acquaintance with me that he would eventually just leave me alone.

Despite being outwardly upbeat and cheerful at work, I would prefer to keep work interactions professional and work related. Has anyone else gone through something like this and what have you done about it? Would it be reasonable for me to express that the way he acts around me feels awkward and how would I express that in such a way that he would stick to strictly professional or work related interactions and just generally leave me alone?

I don't think he's creepy but I just feel that if I don't say anything, it becomes a bit creepier over time when I'm making an effort to avoid him and make myself scarce just so he wouldn't talk to me.