I, personally, would never use this phrase. I would also be rather offended if someone simply assumed that I'd indulge in this sort of superstition.
However, assuming that you absolutely know that someone is religious (say you met them at a church/mosque/synagogue), then a simple, "Would you pray for me?" should suffice, as long as the other person knows what it is you want praying about.
A more secular, and probably just as (non)effective request is, "Wish me luck!" or even "Please think about me today", "Please keep me in your thoughts today."
- For Teachers