EMERGENCY! Missing fish?????????????????? HELP QUICKLY!!!!!!!!!!!!!!!!!!!!!!!… EMERGENCY!?

Ok, so in an outdoor pond (about 3 1/2 ft deep and 8 ft around) i got four 3 inch koi. all was great and dandy, and the net day i got three goldfish. One goldfish was eaten or something, because it wasn't in the pond the next day. (The night before was a huge storm if that helps) a few days later the biggest out of the koi died, we don't no why for sure, we took it to pet-co (for a refund) and they said it was probably the water temp or something like that. (very detailed answer, huh?) the next day we got 3 more awesome pretty goldfish, and while i was feeding all the fish, i noticed one of the koi was missing. I saw it about 3 hours earlier, so i don't no where it went. The second big koi i was feeding went under a little overhang in the water. I went over to my father to tell him bout about the missing koi. When i returned (less than a minute l8r) the big koi was nowhere to be found! at feeding time they all rush over and i can make sure they all appear healthy (no fin rotting and loss in brightness, etc.), and he was just gone! Please help! there are a ton of crack and caves, and about 1/3 of the pond has lots of floating plants. is their any possible way any of the missing ones are alive? Extra info: we aren't keeping the koi in the pod forever, so don't give me any crap about how its not big enough. The water is good and ph kh and all that, and its very clear. There is a waterfall running into it, and a huge filtration system. They didn't get sucked up in that i no for sure, cause we have netting covering the outside of the filter thingy. I just fished out some bullfrog eggs, and no blue heron or raccoons seen YET. oh, and i have no cats. pLEASE HELP! I DO NT WANNA LOOSE ANY MORE FISH! Whats happening! i watch hem all day and have never seen any predators. ( i no there out their tho)