The Love Island star, who was nicknamed Muggy Mike, was found in a forest near his home in Essex on Friday, according to reports.
Thalassitis, a Cypriot, was born in Edmonton in London and played for clubs including St Albans and Chelmsford.
The former League Two footballer enjoyed a successful career in the sport before starring on Love Island in the summer of 2017.
He also appeared on Channel 4's "Celebs Go Dating" in 2018. Please stop brandishing that. My heart and soul and love goes out to his friends & family. "A good guy, taken far, far to soon", he wrote on Twitter.
While Tyla Carr, who was coupled up with Mike during the show, said "I can't believe the call I've just had".
Dom revealed: "You get a psychological evaluation before and after you go on the show but hands down once you are done on the show you don't get any support unless you're number one". 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!
Fans and former team mates have been taking to social media to pay tribute. Mike you absolute gent.
Fenton tweeted: "I'm lost for words". Our thoughts and prayers go to his family and friends at this time.
Mike Thalassitis has sadly passed away just days after his beloved grandmother he lived with passed away.
James Jordan posted: "My heart goes out to his family and friends at this hard time". Mike, you were love by all the Love island family. "You'll be missed so much".
"Met him before and seemed like a top lad.so, so sad". The Only Way Is Essex star Ferne McCann wrote: "So so so so sad".