var bos : GameObject[];
....
function Update () {
      
if(Input.GetButton("Jump")){  

                    bos = GameObject.FindGameObjectsWithTag ("Particle"); //найти все объекты помеченные Tag'ом "Particle"
       
       for (var bo : GameObject in bos)  {  
         myParticles = bo.gameObject.GetComponent(ParticleSystem);  
         myParticles.Stop();            
       }

}

}

function Update () {
           if(Input.GetButtonDown("Jump"))         
               Search();
}
function Search () {
               var bos : GameObject[] = GameObject.FindGameObjectsWithTag("Particle");        
           for (var i = 0; i < bos.Length; i ++)  {         
               bos[i].GetComponent(ParticleSystem).Stop();                   
           }
}