Strictly Come Dancing star James Jordan also spoke out, adding: "So much bad stuff been going on in the world recently and then I just heard that Mike Thalassitis from Love Island died at age 26".
He starred on season three of the ITV show in the summer of 2017 after enjoying a six year career as a footballer.
In a post to Instagram, Mitchell said he was "heartbroken" by news of Thalassitis' death, hailing his "positivity and charisma".
So so so so sad. I'm in shock. Mike you are going to be sorely sorely missed. One of the best people I've ever known taken from us far too soon, I'm heartbroken and can't put into words how much I'm gonna miss you bro! His name was Mike Thalassitis, and every inch of my heart goes out to his family and friends. All my love goes out to your friends and family.
The Love Island star was found in the woods near his Essex home yesterday. Mike, you were love by all the Love island family.
He dated The Only Way Is Essex star Megan McKenna before splitting up previous year, and had appeared on the series Celebs Go Dating in 2018. You were the kindest soul, you were so amusing and you had so much to live for.
After finding fame on Love Island, Mike remained in the public eye and appeared on the 2018 series of Celebs Go Dating.
I have no words.
Alex Bowen and Rachel Fenton, who both also appeared on Love Island, tweeted their respects.
"Our thoughts and deepest condolences are with Mike's family and friends at this very sad time". My heart goes out to his family.
"Everyone connected with Ebbsfleet United is shocked and saddened to learn of the death of our former striker Michael Thalassitis", the statement reads.
And Bowen wrote: "I cant get my head round this RIP brother".