The Clan Hannay Society wants to save the 16th Century Sorbie Tower in Wigtownshire and bring it back into use for future generations.
The society has worked for more than three decades to preserve and make safe the ruins of the building, which was abandoned in the mid 1700s.
Now, around 600 members of the society have been informed of plans to restore the crumbling tower and convert it into holiday accommodation.
Dr David Hannay, clan chief, said: “The problem of conserving historic ruins is that, without continual expenditure, ruins become more ruinous.
“Often the only sustainable option is restoration so that the building can be used. But this requires a realistic and flexible attitude from official bodies.
“Restoring Sorbie Tower is a long term project, which will only be possible with a successful international campaign and work on the tower will be done as funds become available.
“But this work must be guided by the aim of restoration rather than preserving at all costs vestiges of the past. Only in this way will historic buildings such as tower houses be kept alive for future generations.”
However, Dr Hannay added: “There are now signs that these attitudes are changing.”
Historic Environment Scotland recently awarded the Clan Hannay Society just over £15,000 to support emergency repairs of an internal stair wall and the purchase of scaffolding for ongoing maintenance.
The Clan Hannay Society was formed in 1960 for those with the family names of Hannay, Hannah, Hanna, or Hanney and their relatives.
Around half of the society’s 600 members live in the United States.
Sorbie Tower was built in the 16th century for Alexander Hannay of Sorbie, and was occupied until 1748 after which the castle became ruinous.
In 1965 the castle was donated to the Clan Hannay Society and over the next 35 years the clan spent about much time and money on conserving the ruin, but it became dangerous and required scaffolding, Dr Hannay said.
Major repairs were carried out in 2001 and 2005 with funding from the Heritage Lottery Fund, and partnership funds from Clan Hannay and Historic Scotland.
The surrounding woods were cut back in 2007 and in 2010, Historic Scotland agreed to put the tower, which is a Grade A listed scheduled monument, on the register of castles suitable for restoration.
In 2011, a feasibility study concluded that full restoration was the only sustainable option for the future of Sorbie Tower as it would bring in significant income from holiday lets amongst other activities.
The international appeal was earlier launched at a reception at the House of Lords.
The Clan Hannay Society held an event in New York during Tartan Week in April this year to raise support for the project with fundraising work continuing.
Historic Environment Scotland has said enough detail survives about Sorbie Tower to enable an “authentic restoration” of the building.