The Ton boss swooped to bolster his depleted backline after releasing several members of last season's defence.
Moore says he is thrilled to have been able to add 17-year-old centre-half Naismith, left, to his new-look rearguard.
He told the Tele: "We have agreed a deal to sign a young defender on loan from St Mirren for the first six months of next season.
"Jason plays at centre-half, is the St Mirren Under-19s captain and a Scotland youth internationalist. He's very highly-rated and St Mirren manager Danny Lennon was kind enough to give us him on loan.
"Danny's been a good pal of mine since our days playing together at Partick Thistle, and it was because of that friendship that we were able to get Jason. He was happy for him to come to us, so I spoke to Jason on the phone earlier last night and that's when he agreed to come. He is delighted to have this opportunity and is already excited about next season.
"He's a player I've had my eye on for a while. I watched him play for St Mirren a few times this year and he was always very impressive. So I'm delighted to have been able to bring him here."