The former Home And Away and X Factor Australia star has tributes and well wishes flooding in from fellow celebrities and fans alike.
Australian singer/songwriter and fellow X-Factor Australia star, Taylor Henderson, was one of the first to comment on Ruffo's Instagram post.
"I can't believe what I'm reading mate," Taylor commented.
"It's just not sinking in. We're all here for you Johnny and without a doubt... we're all praying for you. Look after yourself big fella!"
"So much love to you. Stay Strong," said friend and X-Factor judge, Natalie Bassingthwaighte.
The Footy Show host, Beau Ryan also sent his love to the battling musician:
"Sending love brother."
Other stars to pledge their love and support for 29-year-old Johnny include Therese Kerr, fellow Home and Away stars Jackson Heywood and Jake Speer plus Survivor's El Rowland.
"Sending you so much love and healing energy, gorgeous soul," Therese Kerr's comment read.
"Sending you lots of love mate. You need anything at all, anytime, you give me a call! Stay strong mate," commented Jake Speer.
Fans have left similar sentiments:
"Have followed your career & all that you do for charity & making people smile. Prayers & love sent while you beat this," said one.
"You will win this battle Johnny - Fight, you are a warrior and win," said another.
This, on top of over 4000 other comments from fans, stars and personalities alike is a testament to just how much Johnny is cherished and how many lives he has touched.
Our thoughts go out to Johnny during this incredibly difficult time.
Earlier this week Johnny Ruffo, 29, took to social media to share the news that he has been diagnosed with brain cancer.
“So I have the news,” he wrote on Instagram. “It was a bit of a shock and I’ve got an interesting journey ahead and a bit of a battle.
“I am starting aggressive treatment for the next few months to fight the diagnosis of brain cancer.
“Please stay positive for me and I’ll try to update you guys on my progress.”