Transform.Forward in 2D

Here is the code:

 using UnityEngine;
 using System.Collections;
 
 public class bulletactions : MonoBehaviour
 {
     private float yposV;
     private float xposV;
     public Rigidbody2D rb;
     private float PLAyposV;
     private float PLAxposV;
 
     // Use this for initialization
     void Start()
     {
         rb = GetComponent<Rigidbody2D>();
         // This stuff makes the object point towards the mouse pointer when it first spawns, but not again.
         var pos = Camera.main.WorldToScreenPoint(transform.position);
         var dir = Input.mousePosition - pos;
         var angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
         transform.rotation = Quaternion.AngleAxis(angle, Vector3.forward);
         //
         PLAyposV = GameObject.Find("Player").GetComponent<PlayerShoot>().playerYpos; //Finding the players X and Y position from another script and then moving the projectile to it.
         PLAxposV = GameObject.Find("Player").GetComponent<PlayerShoot>().playerXpos;
         transform.position = new Vector2(PLAxposV, PLAyposV);
     }
 
     void Update()
     {
         yposV = transform.position.y;
         xposV = transform.position.x;
         transform.position += transform.forward * Time.deltaTime;  // This line
         if (yposV == -200)
             Destroy(gameObject);
         if (yposV == 200)
             Destroy(gameObject);
         if (xposV == -200)
             Destroy(gameObject);
         if (xposV == 200)
             Destroy(gameObject);
     } //If the object goes out of map range, delete it.
 }

What this script is supposed to do: The script is attached to a missile entity that upon being cloned, faces towards the mouse pointer. Then, it will travel a speed of X in the direction it is currently facing until it goes out of the region and is destroyed.

What the script actually does right now The missile appears, rotates correctly, but does not move.

This is because i do not understand how to put transform.position += transform.forward * Time.deltaTime; // This line into action.

Please help! Thanks :)