I have the gene expansion pack and have never seen nor heard of anyone using the new characters nor have i been able to use them any1 help please

There used within the Gene boards. If you look in the common settings it will tell you whether or not their enabled. From there it is a matter of time before your one of them. They are chosen randomly at the begin of each board. One user on one team will be Meryl, and the other team will have a user as Johnny.

The funniest part is going on a kill sreak with Johnny. It causes him to crap his pants, I believe it is every 3 consecutive kills. Make sure your teammates don't follow to close behind for the gas is considered friendly fire. And seriously i'm not kidding about the friendly fire!

they can appear on any map

True, but very few people use them on the old maps. And now with the MEME expansion you can mix and match who plays. I like using Mei Ling the best but a lot of the rooms I've been in lately have been doing the Johnny/Ocelot mix which is pretty fun.