The Disney starlet, 18, topped the list for the second year in a row.
Cyrus - who hit headlines in December when she was caught on video smoking a bong - beat out competition from Lindsay Lohan and Demi Lovato to take the title.
Both Lovato and Lohan entered rehab in the past 12 months.
The poll, by AOL website Just So You Know, was voted for by their core audience of girls aged between nine and 15. Also in the top 10 were Teen Mom star Amber Portwood, rapper Kanye West and Gossip Girl actor Chace Crawford, who was arrested for marijuana possession.