The Loyalist Commission, an umbrella group of unionist politicians, protestant clergy and loyalist community workers and paramilitaries, has called on the UDA to say if it was involved in the disappearance of Alan McCullough last Wednesday.
Mr McCullough, a former close associate of deposed UDA commander Johnny Adair, hasn't been seen since leaving his home in the company of two loyalists.
Police believe he may have been killed as part of an ongoing internal feud within the UDA sparked by the actions of Adair and his supporters in west Belfast.
The PSNI has already launched a murder inquiry, even though the 21-year-old's body has not been found.
Officers searched a reservoir in north Belfast last week as part of the investigation and yesterday seized a fishing vessel in Carrickfergus harbour for forensic examination.