Australian actor Liam, who only joined Twitter in June, is still following his 20-year-old fiancée on the microblogging website.
Since their engagement in May 2012 Miley and Liam have had an on-off relationship.
Three months ago Miley was forced to deny rumours that she was involved with Canadian singer Justin Bieber and Liam has recently come under fire following reports that he has been seeing actress January Jones.
"I'm engaged! I'm engaged. That is impossible," said Miley in a morning interview on Washington DC radio programme The Kane Show.
Miley and Liam, who first met on the set of their film The Last Song in 2009, were last seen in public together in August.
The We Can't Stop singer smiled on her fiancé's arm for the premiere of his new film Paranoia, as the two stepped out at the DGA Theatre in Los Angeles.
The Hunger Games Liam popped the question to the former Hannah Montana star with a 3.5 carat Neil Lane engagement ring.
Although Miley has since been seen with and without her dazzling diamond ring, she had it firmly on her finger at the premiere and following her performance at the VMA Awards.