This!
You can pray however you like but here are some examples...
Short version:
"Dear St. Anthony, please^ come^ around: something^ is^ lost, and^ it^ cannot be found."
Long version:
"St Anthony, perfect imitator of Jesus, who received from God the special power of restoring lost things, grant that I may find [name the item] which has been lost. At least restore to me peace and tranquility of mind, the loss of which has afflicted me even more than my material loss.
"To this favour, I ask another of you: that I may always remain in obsession of the true good that is God. Let me rather lose all things than lose God, my supreme good. Let me never suffer the loss of my greatest treasure, eternal life with God. Amen."
Since moving house I have prayed to St Anthony to find things a few times and not only have I suddenly seen in my minds eye where something is and found it, but I've also found other things I lost which I hadn't prayed about and had forgotten about! My prayers weren't in the formats above, they were "freestyle" prayers, so you can pray however you like!
I hope you find them (or it is revealed to you exactly what happened to them so you can rest)