The Missing wont return for Season 3.
Co-creators Harry and Jack Williams have opted to cancel the mystery thriller after two seasons, but plan to revisit the franchise as a spinoff, per Digital Spy:
Harry: “We want to do something with Tcheky [Karyo, who plays Baptiste] again – we want to keep that character alive. I think we will revisit him in some form or another.
I’d be leaning towards a spin-off, personally. But God knows what any of the channels think.”
Jack: “This is totally just us talking – but we’d like to see Baptiste again, we’d like to revisit the tone and the feel of that world. We don’t want to do it, like, ‘More missing children!’ – but revisiting him, and the feel of The Missing, is something we have started talking about in the last couple of months. So hopefully there may be news on that soon.”
“We were so pleased that people liked The Missing. You don’t want them to be like, ‘Oh, and then they made the third one and it was shit!'”