I simply say, " Dear St. Anthony, please find my .... for me and return it."
Right now, I am hoping he will get round to the gold earing I dropped somewhere last Wednesday.
It sometimes takes him a while though - I forgot my amythist rosary given me by my husband when we got engaged in a hotel bedroom. Phoned the hotel and was told it was no longer there, gave it up for lost, but three weeks later it was sitting in its case, staring me in the face just in front of my three black madonnas. I had most certainly not put it there, nor had it been there when I searched the house for it.
St Rita finds lost property too, and no, you don't need to be Catholic to ask any saint for help, or even Christian for that matter.
As some Frenchman said on his deathbed "God will forgive me, it is what He does." I don't remember who the man was, only that he had been a confirmed atheist all his adult life.