Sayyed Mohammad Al-Musawi, Sayyed Mohammad al-Musawi is originally from Iraq and heads up the World Ahlul Bayt Islamic League in London. Other than being involved in various humanitarian projects, he frequently responds to... Answer updated 4 months ago

1. Many persons who claim to be atheist do so with out real thinking but just for psychological  reasons like to oppose the family or the atmosphere or to look like different or to show that they are modern ,etc.

We should not take their claim as a studied intellectual decision, unless we discuss with them in neutral atmosphere with out any challenge or instigation.

2. If you are sure that a person has become an atheist, you should look at the reasons and try to understand the background of the situation. 
3. We need to see and assess his arguments and the authority which he believes in, e,g. Intellect or reason, or science etc. We must talk to him in the language which he understands. Those who claim believing in logic and reason, should be given evidence based on logic and reason. We as followers of the Real Islam of the Prophet (SAWA) and Ahlul Bayt (AS) have the richest treasure of intellectual and logical evidence.

4. Invite them for dialogue and debate based on what they claim to believe in and be patient and tolerant.

5. Never expect them to accept your evidence right away. They might reject it verbally but keep thinking about it for sometime. Give them the time which they require and keep on presenting the evidence now and then in a polite and respectable way.

6. If an atheist invites other to be like him, you can keep logical principles and rational thinking as your weapon to easily refute his claims and proof him wrong. Never insult nor attack him but counter his argument with logical and rational evidence with etiquette and respect.

7. If the person respects noble personalities like the Prophet Muhammad (S) or Imam Ali (A) or Imam Husain (A), you can remind him with life and sayings of these great leaders who had the maximum level of intellect.

8. Always keep the doors open for dialogue and never lose hope. No one knows when the heart and mind will open and becomes able to see the truth.

Wassalam.