In a post on the micro-blogging site, which has since been deleted, Amanda, 27, used her frequent insult on the 'Lucky One' actor, calling him “ugly”.
She wrote: “@ZacEfron has an ugly face (sic).”
Zac isn't the only celebrity to face Amanda's wrath, she previously claimed Chris Brown assaulted his then girlfriend Rihanna in 2009 because she wasn't pretty enough.
She tweeted: "Chris Brown beat you because you're not pretty enough," before adding: "@Rihanna no one wants to be your lover so you call everyone and their mother that I almost named my new dog Rihanna (sic)."
She also lashed out at Rihanna's ex Drake, calling him “ugly”, despite previously opening up about her crush on him.
Amanda said: "Drake has the ugliest smile, ugly gums uneven teeth ugly eyes," before deleting the tweet.
However, she later took to her Twitter account to add: "I won't deny calling @drake ugly,” before appearing to regret her tweets.
She wrote: "I'm sorry about the tweets I said about @drake I didn't mean what I said. I hope to become friends with him instead of smashing him!"