The funnyman announced last year he had begun work on another sequel following the success of the first three installments, which grossed $676 million at the worldwide box office.
Myers insists the project is still "on track" but admits he has run into problems recruiting stars for the next movie.
He tells MTV News, "Things are on track. It's hard to keep a... team together and I'm very happy how insanely well it's gone. Then it gets hard to get everybody all together. (But) it's chugging along."
Director Jay Roach confirmed last month he will be back to helm the next big screen outing.