I know how frustrating it is when your frogs disappear! Slightly different but I have African Dwarf Frogs and had to move them out of my main tank while I dosed for worms. The biggest, fattest one just completely disappeared one day. I tore that tank apart several times looking for her, there was nowhere she could've jumped out and I never found a body, just completely gone. I actually tore that tank down today to return them back to the main tank and was still looking in vain hope I'd find her, but no joy.