Parsons said: “It’s a wonderful survivor of the golden years of cinema, those glory days of the ’30s when cinema was an escape from a very sort of grey world into this glamorous haven.”
He said the Art Deco building had “always been this wonderful building and it’s been much loved by generation upon generation”.
The party is being held from 13:00 to 18:00 BST on Saturday.
Parsons added: “If we don’t save it now I think it’s in grave danger of being demolished and lost forever.”
The cinema, which opened in 1938, was slightly damaged in March 1941 during the air raids on Plymouth.
Parsons said it gave people “that small escape” from the horrors of World War Two.
It later had a third screen and a bingo hall added.
Volunteer Caroline Blacker said, as part of an oral history project to preserve stories of the venue’s past, the campaign group wanted to record people’s “memories attached to this building, particularly when they were teenagers and they went to see the live music” there.