How do I approach a guy I have no bussiness with?

My eye fell on someone at school from a different department, and I have no excuse to talk to them and I rarely see them. In this case they also aren?t (much) on social media.
How do I as a woman approach this guy and show that I?m interested without acting like a stalker?
Edit: I already know this person because we worked together before but I haven?t worked with him for a year now. I couldn?t pursue at the time because I was in a relationship. (I don?t know if he?s in a relationship or not)
Edit 2: for people wondering exactly how I know him, I?m a student and he works for the school I go to, he?s not my teacher tho. Which makes it a little harder for me to approach him in front of everyone (and his colleagues) hope this clarifies things. I?m not from the US so things work a little different here if anybody is confused about what?s allowed and whatnot
Edit 3: *typical im so overwhelmed by all the messages comment. But no, I really am, and I?m reading every single one. For those interested, I did approach him before to ask if he has a pen ? the person next to him gave me one before he could answer me and he just gave me a glassy look and I was gone because I interrupted their conversation ?. The only hint I have that he might be interested is that he once asked me if a guy I was hanging out with was my bf.


Source.