The 15-year-old's uncle paid tribute to a “big, strong, special man” while his school said the world has lost a student “full of potential”.
Police said they believe a body discovered during searches in Fintona on Monday morning is that of Matthew McCallan, and the death is being treated as unexplained.
On Monday night, his devastated mum Frances said her 15-year-old boy is now an angel in heaven.
"To all the wonderful people who came out to help look for my beautiful son, you were amazing and the community spirit was unbelievable,” she posted on social media. "I can’t thank you all enough.
"He is now an angel in heaven and is going to be missed so much by his mummy, daddy, and loving family.
"Sleep tight, my darling.”
Tributes were also posted by Matthew’s uncle who hailed him as a “big, strong, special McCallan man” who “left us too soon”.
"Great lad, great nephew,” he added.
And in a tweet, Sinn Fein vice president Michelle O'Neill added: “My thoughts and prayers are with the family of young Matthew McCallan this evening.
"Heartbreaking and unimaginable news for his mummy, daddy and wider family and friends circle. Sending you all our love.”
The 15-year-old from Dungannon was last seen at around 1.20am on Sunday in the village where he had attended a social event in the Ecclesville Centre.
The venue is two miles away from where his body was found.
Matthew was a Year 12 pupil at St Patrick's College, Dungannon. A post on the school’s Facebook page expressed shock and sadness at the news.
“Today brought the worst possible outcome for the parents, family, friends and our school community – to have lost Matthew so tragically, we are just devastated,” it read.
“Matthew was a quiet boy, not overly confident – a young man still growing into his skin.
"He had a slow smile, that spread and lit up his face, then the twinkle hit his eyes.
"He was a young person who loved the practicalities of learning – opting to study construction, engineering and road traffic studies.”
The school said Matthew enjoyed nothing better than being in the workshop getting the chance to develop his skills.
“For Christmas his father had only just bought him a toolbox – he would have so loved that,” the post continued.
“We have not just lost a member of our school community, the world has lost a young man full of potential, ready and eager to start out on his journey of life and work.”
The school offered condolences to Matthew’s mother Frances and his father Peter.
"He was the apple of their eye,” the post added.
“They need our prayers now to face the days ahead.
"His family have lost a grandchild, a nephew, a cousin, his friends have lost a loyal, witty companion, who was supposed to be with them for so much longer.”
The school chaplain and the Education Authority’s Critical Incident Management Team will be on campus over the next few days to offer counselling and support to students and staff.
PSNI Detective Inspector Michael Winters said the thoughts of police are “very much with Matthew's devastated family”.
"A number of specially trained officers are providing support to them at this time,” he added.
"Detectives will continue to investigate the circumstances surrounding the death, which is currently being treated as unexplained.”
A missing person report was made shortly after 3.30am on Sunday when Matthew did not arrive home.
DI Winters added: "Sadly a body, which we believe to be Matthew, was discovered in a ditch in the laneway of a property approximately two miles away from the social event at 11.45am today.
"We are keeping an open mind and would appeal for anyone with information to come forward.
Police have urged anyone who can help trace the boy’s final movements, or who has CCTV or dashcam footage, to contact detectives on 101.
PSNI vehicles were stationed on the Tattyreagh Road just outside the village where searches took place earlier on Monday.
Matthew was last spotted at around 1.20am on Sunday after leaving a what is believed to have been a Christmas event.
West Tyrone MLA Nicola Brogan offered her deepest and heartfelt sympathy to the family of the deceased and to everyone who knew him following their “heart-breaking” loss.
“His death at such a young age has shocked and saddened the entire community,” she said.
“I would also like to pay tribute to the community and everyone who joined in the search for Matthew.
“I would encourage anyone with information that could help the police in their investigation to bring it forward.”
Omagh councillor Stephen Donnelly also praised those who helped in the search and offered condolences to Matthew’s family.
"There is little that words can do to capture the sheer devastation when a teenager never again returns home to their family, and their life ends just when it should only be beginning,” he wrote on social media.
"My gratitude is with those in our local GAA and wider society who worked hard in Fintona to bring Matthew McCallan home.
"Our thoughts as a community belong to his family as they now come to terms with the unthinkable.”
Fintona Pearses’ GAA club helped organise a community search effort but took to social media a short time after it began at 9am on Monday to announce it had been suspended and thank everyone who offered assistance.
It was previously reported that Matthew was last seen on CCTV outside a takeaway in the Fintona area getting into a grey car with a man wearing a black body warmer jacket.
He also was allegedly seen speaking to a taxi driver in a red car, whom his family are appealing to come forward should he have information about where Matthew was possibly headed.