हद पार बेहद है, बेहद पार अक्षर,
अक्षर पार अक्षरातीत, जागिये इन घर ॥

Beyond this perishable, timed and limited world exists indestructible, eternal and infinite, abode of Akshar Brahma. Beyond Akshar is Aksharatit, Wake up souls in this home.

how to influence

Why you want your friend to change his view regarding God? Is it that you are uncomfortable that your friend is atheist where as you are not. Then try to understand your own standing or view point. Why do you believe in God? How important it is for you? How it has helped you? Why you cannot accept that your friend must stay an atheist? Also understand whether you are doing all this to comfort yourself or for your friend's best interest. You can do little on others if it is for your own self.

Understand Friend's Beliefs : Try to understand their beliefs, why they feel to believe in God is not important. What are your friend's logic. Sometimes, a person with strong family, healthy body who has got lots of good qualities feels God is not necessary. The time is the best teacher for some, patience is the best policy here.
Listening is as important as preaching.
Before trying to convince others about God, first you must convince yourself totally must try to get genuine experience and not depend upon other people's experience.
If you are too concerned then Pray to God in the heart of heart for your friend.

Get the facts about your beliefs, everything that you feel important, study that very well.

Then Discuss.
Wind, Water, Energy and Space that we need to live are all colorless, tasteless and odorless. They all can be sensed by the external senses and conveyed to the mind. But God can be experienced within and external senses and the mind cannot conceive it.

If one does not agree on believing God, you can try the Self. Understand the self, loving the self, nurturing the self within (Nij), trying to make yourself happy is finding what is true happiness. Is shopping more joyful or trekking in the mountain which one is long lasting... the true happiness are cherished in the heart forever. The happiness that does not last long or can put one's self in trouble like drinking, smoking etcs must be avoided. If one believes in God but does not believe in the ones' self then that belief has no meaning. Also one believes in God, he does all sorts of wrong things derives no benefit from believing in God.
First one has to deeply love one's own self and do all the things that bring everlasting happiness, when the soul is happy it becomes grateful and wants to express the gratitude at that very moment it will search for God. Such transformation is far far better than a person who constantly lived in fear of God's punishment by birth and did not do wrong not out of the self intellect but out of fear of God.
Our existence itself, the life in the earth all that is living that is aware of its living is God. We are tiny particles of God we lose the attributes because we forget about it or desire to pursue something external like a car or shoes. Analyze ourselves like what makes us sad, mad, glad and what thoughts are processed in the mind, from where the thoughts are generated, they are positive or negative.

Even if you feel God inside out, you cannot convince a person who is too much enmeshed in the worldly pain/pleasure, joy and sorrow. The mind has to be totally empty and detached from the worldly affairs like the working of Sun or God himself. You cannot give anything unless that person deserves or that person wants to accept the gift that you have. Giving forcefully does not help either. You can give a book to read, but the person has to read it himself.

Reading books like the Power of Subconscious mind or books by Napoleon Hill will also help. Try to understand the self awareness, understanding of subconscious mind and love all these are attributes of God itself. If you are with the God or experience God within you do not have to believe in God!

Warning: Do not think your friends' belief are all wrong. Cherish your friends’ difference in thinking. Keep wishing well.

Let go:
After all you did and tried then let go. Shri Krishna tried hard to change Duryodhana but failed and said he could change the present but not the prarabhdha the past actions which gives you the intellect about right and wrong, how to control the senses and etcs. It is not easy to change the habit of the mind, it needs proper support, reasoning, will power and internal and external conditions. So many factors are responsible for a person to progress or degrade. A very acute mind can deal external conditions well while a weak mind cannot.