How to make an enemy teleport?

 var vel_vec : Vector3;
 var speed : float;
 var distance_byte : float;
 var player_life : Player_life_script;
 var close :boolean;
 
 
 var following:boolean;
 var spawnTimer:int;
 var spawn:boolean;
 var timer:float;
 var fader:float;
 var fadeOut:boolean;
 var fadeIn:boolean;
 var target : Transform;
 var pos:Vector3[]=new Vector3[5]; //Here you need to fill the array with some various vector3
 
 function Start(){
    pos[0]=new Vector3(x,y,x);  //Here intead of x,y,z put the appropriate positions
    pos[1]=new Vector3(x,y,x);
    pos[2]=new Vector3(x,y,x);
    pos[3]=new Vector3(x,y,x);
    pos[4]=new Vector3(x,y,x);
    target = GameObject.Find("Player").transform;
 }
 
 
 function Update(){
    if(close){
       following = true;
       vel_vec = target.position - transform.position; // creates the vector from the enemy to you.
       transform.LookAt(target); // enemy looks to you
       transform.Translate(Vector3.forward * speed * Time.deltaTime); // enemy walks to you
       if (vel_vec.magnitude <= distance_byte) //if is near{
           animation.Play("byte", PlayMode.StopAll);
           player_life.hp -= 1;
           vel_vec = Vector3.zero;
       }else if (vel_vec.magnitude > distance_byte + 5) // if is far
          animation.Play("walk", PlayMode.StopAll);
     }else 
        // Add codes that gets your Alien from a waypoint to another randomly to create an effect of wandering.
       
    if(following){   
       timer += Time.deltaTime;
       if(!spawn){   // Get a random int for defining when the nPC is teleporting
           spawnTimer = Random.Range(1,6);
           spawn = false;
       }
       if(timer>spawnTimer){  // Check if the timer is greater than the random value
          fadeOut = true;
       }
       if (fadeOut)FadingOut();
       else if (fadeIn) FadingIn();
    }
 }
 
 function FadingOut(){  
    renderer.material.color.a-=Time.deltaTime;    // The NPC slowly disappear
    if(renderer.material.color.a < 0.1){        // If almost gone 
       transform.position = FindClosestTarget();//Here calling function
       fadeOut = false;                         
       fadeIn = true;
    }
 }
 function FadingIn(){  
    renderer.material.color.a+=Time.deltaTime;   //NPC appears slowly   
    if(renderer.material.color.a>0.99){         // If NPC is fully in
       fadeIn = false;                          // All var set back to initial
       timer = 0.0;
       spawn = false;
       following = false;                    // The NPC is then not following anymore
    }
 }
 function FindClosestTarget () : Vector3 {
     var closest : Vector3; 
     var distance = Mathf.Infinity;  
     for (var i:int = 0; i < 5; i ++ )  { //Iterating through all target and defining the closest to the target/player
         var diff = (target.position - pos[i]);
         var curDistance = diff.sqrMagnitude; 
         if (curDistance < distance) { 
             closest = pos[i]; 
             distance = curDistance; 
         } 
     } 
     return closest;    
 }
 function OnTriggerEnter(other:Collider){
    if(other.gameObject.tag == "Player") close = true;
 }
 function OnTriggerExit(other:Collider){
    if(other.gameObject.tag == "Player") close = false;
 }

Ok I added your part of the script. You need to add a sphere collider set to Is Trigger to your alien. When your player steps inside the wone the alien will cahse him. While chasing the following script will trigger until you manage to either kill him or run away out of the sphere zone.You still need to add the part where your alien is wandering around when is not chasing you.