The key idea is that our thoughts control how we feel, not the events or surroundings of our lives. A person who is considering suicide often has a very different view of events because of their thought process. The idea of CBT is to change the way you think and by doing so you are able to feel differently about the events in your life.
However, I would never suggest that someone simply start applying CBT on their own with out some guidance. I am very nervous about how you want to make this a social application. Depression can be a very personal and embarrassing disease for a person and even positive encouragement can cause more depression.
Lets say we have a kid named Stan. Stan is a very depressed kid who is considering suicide. He manages to let his friend Bobby know that he has been considering killing himself. Bobby is shocked as Stan is a very bright and successful kid. Bobby tells Stan that he 'can't believe that Stan would want to do such a thing' and that 'he has so much to live for.' Bobby thinks that he is helping Stan, but Stan views this very differently. Stan thinks, 'No one understands me, Bobby is just saying that to make me feel better.' While the temporary relief of telling someone was something that Stan really wanted to do, in the end it only ends up making him feel more depressed.
The reason behind this sort of thinking is because of the Cognitive Distortions. Stan's perception of reality is vastly different because of them. It is for this reason that I am concerned about how you make this a social application. In my opinion the best thing you can do for a person who is considering suicide is to get them to a trained professional.