All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
First of all, you should know that calling people to Allaah is one of the greatest acts of worship by which one gets nearer to Allaah, as Allaah Says (what means): {And who is better in speech than he who [says: "My Lord is Allaah (believes in His Oneness)", stands straight (acts upon His Order)] invites (people) to Allaah's Islamic Monotheism, does righteous deeds, and says: "I am one of the Muslims.}[Quran 41:33]. Furthermore, it is confirmed that the Prophet said: "I swear by Allaah! If Allaah guides one single man (to Islam) by your efforts, that will be better for you than possessing an abundant number of red camels (a very expensive breed of camels)." [Al-Bukhari and Muslim]
Being mocked and made fun of by the people whom a person calls to Allaah should not prevent him from continuing to perform this great act of worship. Indeed all the Prophets were mocked by their people; Allaah Says (what means): {There did not come to them any messenger except that they used to ridicule him.}[Quran 36:30]. The fact that the Prophets were mocked by their people did not stop them from calling people to Allaah. For instance, the Prophet was severely harmed and very much mocked but he persisted in calling people to Allaah and Allaah ordered him to be patient in doing so. Allaah Says (what means): {So be patient, [O Muhammad ], as were the messengers of strong will.}[Quran 46:35].
Likewise, a caller to Allaah should be patient.
Nevertheless, it should be noted here that calling people to Allaah in general, and especially the non-Muslims, requires the caller to Allaah to have enough knowledge so that he could clarify the evidence to them and refute arising misconceptions. So, if you think that you are equipped with enough knowledge, then we advise you to call your non-Muslim colleagues as Allaah may save them from Hellfire on the Day of Judgement, thanks to you, and whatever good they did and their embracing Islam will be added to the record of your good deeds. However, if you know that you do not have enough knowledge, you may gift them some beneficial books designed for calling the non-Muslims. You may seek the help of some Muslims in calling them to Allaah, and you should do your best in this regard. We ask Allaah to enable you to do good.
For more benefit on the characteristics of a caller to Allaah, please refer to Fatwa 85108, and for how to call the non-Muslims to Islam, please refer to Fatwa 84345.