How to counter "appeal to faith"?

My friends use 'faith' as evidence for the existence of God. I tried to persuade them but they just said that faith is simply beyond reason. I want to know how to counter their way of thinking. What are the ways I should do to make them realize that they're wrong?

We see this quite often, and as you mention in your question, the position is actually one that abandons reason. Faith is beyond reason as guessing is beyond knowing. The best way to get those who commit this fallacy to see it as a fallacy, is to ask them if other people's faith in other gods is also considered evidence. Then ask them how we can tell whose faith is correct. Clearly, if we are "beyond" reason the very exercise of trying to tell whose faith is correct is moot because faith has already been defined in this context as beyond reason.

In your question, you clearly stated that the person said "faith is simply beyond reason." However, many atheists are often guilty of assuming that when Christians or other religious groups use the word "faith," they actually mean something along the lines of belief without evidence. In fact, many Christians (mostly on the more liberal end of the spectrum) mean something more along the lines of "trust with good reason." Attempting to square this kind of "faith" with the Christian Bible can be quite an interesting topic of debate.

A belief is an idea we hold to be true. Does it have to be true? No. Faith is essentially confidence that one's beliefs are true (objectively speaking, see: Santa Clause, elves, fairies, and myths as examples of beliefs). Because beliefs are the foundation of faith, and because they do not have to be true, it makes sense then that one's faith may not be factual.

Faith has its reasons......bwhahahah