goodlife; Not believing in an interventionist God does not necessarily negate a belief in God or indeed the efficacy of prayer.
In the broadest sense, to pray is to make a request in a humble manner. The term to pray is now mostly used to refer to religious prayers: to commune with a spirit or deity that you believe in. While the rituals and conventions of prayer may vary widely, for example, in Buddhism, meditation is the accepted standard form of prayer, but the intention is the same--to renew one's spiritual connection with a power outside of oneself.
If it brings comfort to believe that divine intervention is a possibility, then it does no harm, and it can do good;
If everyone genuinely wanted peace and was prepared to pray for it, it would no doubt be achievable.