The brutal attack happened at a house in the Ravara Close area of Newtownards last night, Sunday, May 5.
Detective Constable Rea said: “We received a report, just after 11.15 pm, that four masked men had entered the property.
“Three teenage girls were locked in a room, while the male occupant was seriously assaulted.
“It’s reported that he was hit over the head with a hammer and beaten with a pole containing nails.
“We attended the scene along with colleagues from the Northern Ireland Ambulance Service.
“The man sustained a large cut to the top of his head and puncture wounds to his arms.
“All have been left badly shocked and we are appealing to anyone with information, or who noticed any suspicious activity or vehicles in the area around that time, to contact us on the non-emergency number 101, quoting reference 1650 of 05/05/19.”
Alternatively, information can be provided to the independent charity Crimestoppers on 0800 555 111, which is 100% anonymous and gives people the power to speak up and stop crime.