The victim, who has been named locally as Jason McGovern, was from Co Monaghan in the Republic of Ireland.
Police said he made his way home after the attack, which took place outside licensed premises on Kevlin Road in Omagh at around 2am on Monday.
His body was discovered in a friend's house in Emyvale, Co Monaghan after midday on New Year's Eve.
The scene at Emyvale was sealed off for a full Garda technical examination, as PSNI and the Garda investigate the circumstances surrounding the death.
A PSNI spokesman said: "Police in Omagh believe that the deceased was assaulted by a male of stocky build with ginger or blond-coloured hair and would urge this male to contact them in Omagh to assist with their inquiries."
UUP MLA for West Tyrone Ross Hussey said it is believed Mr McGovern was assaulted twice during a night out in the town.
At a time when most people are celebrating Christmas and the opportunities of a New Year, Mr McGovern`s family are faced with the dreadful loss of a son.
"If anyone in Omagh or farther afield has any information, no matter how insignificant that it may seem, they should contact the PSNI or Gardai immediately,' Mr Hussey added.
West Tyrone Sinn Féin MLA Declan McAleer said the victim was the youngest of three boys.
"I am very disturbed that he was the victim of such an attack in Omagh and I am also very concerned about the increasing level of drink fuelled crime in our community," he said.
'This is devastating news for the McGovern family. The loss of a loved one is terrible at any time of the year but made more poignant as it coincides with the beginning of the New Year," he added.
A post-mortem examination is due to conducted to establish a cause of death.
"No further information is available at this stage," a Garda spokesman said.