If you just added them recently they may take awhile to come out, especially if you have more active fish like the neons in your tank. I have 5 in my 120 gallon along with pretty active fish like platies, mollies, neons and clown loaches. They all huddle together in one of the planted corners of my tanks. It is a fake plastic plant along with some sort of tall plant that I am not sure the name of (sorry, not too good with plant names) They also hide in a rainbow rock I got along time ago for my 29 gallon set-up. It has two 3 inch long holes in it and the just hide there when startled, they feel safe there.
When I bought the recent 4 (I only had one previously because all of the others died on me

) they didn't come out at all and hid for about a week. They didn't come out for food and I was scared they would starve. I would put some flakes under the filter and make sure they would sink to the bottom where they hung out in the tank at night. After about a week, they are coming out at feeding time and even coming to the surface to snatch a bloodworm or a flake at the top of the tank.

Some prefer sucking up the leftovers at the bottom and some prefer coming to the middle or top of the tank to eat.
A way you can check if you glass cats are getting enough food is to check their "silver bags" that is their stomach. If it looks empty, they probably haven't been eating, but this is normal or atleast IME for them not to eat or really come out for a few days until they get used to their new home. If it is really fat that means your glass cats are pigging out when you're not looking!
Hope that helped a little. And hey, I titled my thread that because I had to! It posted twice by accident.
