The Black Eyed Peas star lost out in the final on Saturday night with his act Lucy O'Byrne to Ricky Wilson and Stevie McCrorie.
Many claimed that the Irish operatic performer had been "robbed" and techno fan Will was of course on Twitter within seconds, joining them in complaining.
He wrote: "I wish Twitter was the way we voted..."
Will added: "She wasn't robbed....we just weren't voting on Twitter for us to all see It in real time"
The rapper later wrote on his 13 million followers: "I still love Stevie... He's dope...congrats #teamRICKY"
Meanwhile, Will.i.am has also hit out at show bosses for this year's format change that meant not every coach was guaranteed an act in the final.
Rita Ora was left with no team after the second live show after all of her acts were eliminated.
"It’s not fair. I don’t like the new rule," Will said. “I wouldn’t allow a coach not to have someone from her team in the final.”
However Will insisted that he still wanted to be back for a fifth series next year.
He said at the weekend: "At the end of the day, The Voice is a fun format and I love hanging around aspirational singers who want to dive into this world. If I can help them on their way, why not be around fresh new excitement when everyone in my world is jaded?”