Man Im really sorry about your fish. Thats a big loss...I wonder if theres a bacteria thing? Did you clean the plants? Cuz I mean we all bought stuff from there right? Maybe not from THAT tank but I dunno how they are with crosscontamination.
You can't starve them. They can survive months without feeding.
Your only options are to:
1) catch them all
2) or add a fish that will eat them, like a big loach, oscar, ...
3) or tear down the tank, throw away the substrate, and probably the plants too
4) or use the clout medicine. This will make your tank permanently unsafe for shrimps and snails.
When I got some, I've been lucky option 1) worked for me.
Hey PTR, clout - why permanently? Cant water change it out? I ask because we storeordered them for use and uhhh..thats not good to know.