I know 2.(Smallworlds.com and Woozworld.com)
It is poptropica.
This is a opinion question, but the Cheerleading Worlds showcase teams from around the country, the USA teams get 1st place
nikohill
Weeworld and meez.
The Cheerleading Worlds
ONVERSE!it is the best virtual world sign up here
club penguin is the best! also there is panfu
A popular one is FreeRealms.
There.com(the best)Second Life KanevaZwinky
Fantage.com secondlife.com ourworld.com
Never
Facebook would probably be the best