Two search teams have been deployed in Moira, Co Down, on Thursday evening.
At least six people were seen making their way along the Lurgan Road that joins the village to Magheralin shortly after 7pm.
It is understood that police and volunteers have been in the area since around 3pm, after the PSNI shared that they “are growing increasingly concerned about the welfare of 46-year-old man, Philip Porter”.
In an appeal for information issued on Thursday, a police spokesperson said: “Philip was last seen this morning at 2am in the vicinity of Moira. Philip was last seen wearing navy blue trousers, a dark jacket, with a green and black shirt.
“If you have seen this male or have any information on his whereabouts, no matter how insignificant it may seem, please make contact with police on 101 quoting reference 438 05/12/24.”