If you are interested in joining these type of illegal groups, you should find your way to the altcoin forums.
There must be atleast 10 groups active at the moment, though, not all of them are making a profit / successfully manipulating the markets.
Most have a joining fee of a couple of bitcoins as well.
So is it illegal?
I think for some group who play big on both BTC or ALTcoin market is not illegal.
Because when they want to make price down, some people can always buying on them.
And when they want to make price high (this is usually happen) some people will sell more higher than them.
The suck thing is when they controlled in long period. Sell all their coin from
Ex:
1
1.1
1.2
1.3
1.4
1.5
1.7
2.1 (surely they will buy everything people sell until their run off the money).