First spot him. Then turn your body towards him. Then put one foot in front of the other until he is right in front of you and say, "Hey, how's it going (insert name)?" [Or something along these lines]. After that you might ask him to get a drink or dinner after work. "I'm stopping by at (insert place) after work. Want to go?"
Most Helpful Girl
Just casually ask him to hang out together after work. It won't be that hard.