Take a look at AUM 100, I've made an example of flamethrower via particles. They can detect objects and decrease their health. I hope it will help you, good luck.
i create some particles and wanna select them with the mouse like drag and drop the solution i find for now is to use the distance of the particle pos.x and the hit.x of a trace
now i calculate wich particle is the closest to the hit.x with vec_dist, works for now but primitive a bit
hm.. why dont you use sprites instead of particles then? take a look at the samples folder, there should be example that creates same effect with particles and sprites, I guess it will help you