Question

draw a ray diagram to explain the formation of a virtual image of a point source in a plane mirror

Answer 1

I think this is what you are asking. In the following crude drawing, the mirror is vertical, there are two rays that would converge to the right of the mirror to form an image of the tip of the arrow, hence a virtual object for the mirror. By the way, you said "virtual object placed in front of it"; the virtual object is behind the mirror, otherwise rays would diverge from your "virtual object" and you would have the first case you mentioned, a real object. The actual rays reflect at the mirror and converge to a real image of the arrow tip to the left of the mirror.