Cyrus, 23, who was expected to perform at the party in honor of "Hands of Love," her gay rights anthem from the film "Freeheld," was busy rekindling her romance with ex-fiance, reported E! online.
Songwriter Linda Perry announced that "Wrecking Ball" hitmaker could not make it because she was still in Australia.
Perry performed during the party as did Courtney Love, Juliette Lewis, The Cult's Ian Asbury and Christina Aguilera.
The reports of Cyrus and the "Hunger Games" star reuniting came after they were spotted in Australia "cuddling and kissing" at the Falls Music Festival in Byron Bay.