Sorry, it sounds like they most likely got eaten. If you want to breed livebearers I recommend setting up a cheap 2-5g tank and place the preggo females in there. The females have a burst of hormone that USUALLY stops them from eating for at leats a few hours after the fry are born. So if you keep a close eye on mum you can usually catch her before her hormones wear off. I did this with both my Mollies, Platies and Guppies and never had a problem. Its also less stressful then a breeding net and easier to just remove the mum and let the fry grow up in the tiny tank.