Hi Rani,
A shy and introverted guy will often find it easier to open up to someone when they have common interests with that person.
If you have learned some facts about him through the conversations that you have had with him thus far, think about whether you can relate to something that you learned.
If you can, try talking to him about that particular interest and use your own personal stories to draw similarities to it.
This may help to make him feel like you are someone who understands him.
This realization alone could help him start opening up to you, leading him to feel a lot more compelled to come over and talk to you at work as much as he can.