It can be anyone on a social media site. Cyber bullies often try to hide their identities by using fake names so that they can spread misinformation, name call, start a rumor, or just be downright mean to see what kind of reaction they can get. These bullies usually attack more than once and sometimes will try to gain a person's trust first by starting off as if they are a casual friend, and striking when you least expect it.
Adults and children alike can be cyber bullied. Don't give any of your passwords to anyone, be selective in who you chat with, and report any harrassing or th threatening behavior to the social media site or even a trusted adult if it becomes an issue.