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
Weeworld and meez.
nikohill
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.
Fantage.com secondlife.com ourworld.com
There.com(the best)Second Life KanevaZwinky
Never
Facebook would probably be the best