The Black Eyed Peas star gave his thoughts on the current state of the show from his seat during the show's live semi-final on Saturday night (June 15).
He tweeted: "We have to have a superstar this year......a super star needs to come from this show or this show didn't succeed...we need the people help.
"We need to find and define the next big superstar from this show."
The reality competition has fallen to new lows during its second series, with viewer numbers plummeting by 21.7% earlier this month.
Former contestant Bo Bruce also revealed last week she believes Voice UK acts are doomed to fail after the show due to bad management and promotion by the BBC.
Photo gallery - The Voice UK semi-final: