Police have launched an appeal to the 18-year-old after he was last seen leaving a nightclub in Leicester Square, shortly after midnight on Tuesday evening into Wednesday morning.
A student at Dublin City University, Patrick was in London on a theatre trip with the drama club, visiting a number of shows this week.
But the teenager has not been seen since leaving Zoo Bar in Bear Street, Leicester Square, to go to a nearby Burger King restaurant.
Mairin Miller, a family friend, said his family were very worried about him, and were using social media to try and spread the word about him as far as they could.
— Love Belfast (@love_belfast) February 6, 2014
The 22-year-old graduate, who lives in London, told London24 his father and sister are trying to fly over to the capital from their family home in Galway as police search to find him.
“There are no answers, and that’s what’s so upsetting,” Mairin said. “He’s a lovely guy and he would never get into trouble, but we just don’t know what’s happened.”
His sister Regina Ní hAilpín told the Irish Independent it was Patrick’s first time out of the country with a group of friends, and said police are tracking his phone and trawling through CCTV to try and find him.
She added: “He’s young, he’s naive. And London’s very different to Dublin.”
A spokesman for the Met said Patrick, who is white with light brown hair and speaks with an Irish accent, was last seen wearing blue jeans and a blue T-shirt.
Anyone with information is asked to contact police on 101, or call Crimestoppers anonymously on 0800 555 111.