The body of 49-year-old Michael Freshwater was discovered in Westridge Road on 29 April.
Police said they wanted to trace Tristan Pope, 23, and Kevin Suika, 21, in connection with the murder.
They are believed to be from London but have contacts in Southampton and the South East.
Eleven arrests have been made in connection with Mr Freshwater's death.
Ashton Singh, 26, charged with perverting the course of justice, appeared at the city's magistrates' court on 3 May and was remanded in custody.
Two men are being sought by detectives investigating the murder of a man who was found stabbed at a flat in Southampton.