Usually, one of the genders in an opposite-sex friendship is secretly attracted to the other.
Men and women are just different in how they see each other.
Biologically, we are built to procreate.
To this end, having a close friendship with someone of the opposite sex is essentially playing Russian roulette with the likelihood that someone has or develops an attraction for the other.
The body language you exhibit is the one thing that factors tremendously, whether you are dealing with a shy or outgoing guy.
A shy guy is usually looking for lots of positive body language cues from a girl so as to develop the courage to talk to her and ask her out.
And even this isn’t guaranteed.
Nonetheless, any chance at getting a shy or introverted guy to ask you out requires that you make him feel as comfortable as possible with the idea of approaching and talking to you.