enemy detection in 2d

hello all
I want to enemies follow my player in 2d ,I used this code but i dont know why enemy doesnt do anything?

Code (CSharp):

1.  
2. public class Enemy : MonoBehaviour
3. {
4.     Rigidbody2D rg;
5.     Animator anim;
6.     float dirx, walkspeed = 5f;
7.     bool isHurting, isDead;
8.  
9.     public float speed;
10.     private Transform target;
11.  
12.     void start() {
13.     target=GameObject.FindGameObjectWithTag("Player").GetComponent<Transform>();
14.     rg = GetComponent<Rigidbody2D>();
15.     anim = GetComponent<Animator>();
16.     }
17.  
18.     void Update()
19.     {
20.  
21.  
22.  
23.             transform.position = Vector2.MoveTowards(transform.position, target.position, speed * Time.deltaTime);
24.  
25.  
26.             dirx = Input.GetAxisRaw("Horizontal") * walkspeed;
27.  
28.             anim.SetBool("isWalking", true);
29.     }
30.  
31. }

 

Well "it doesn't work" does not tell me much, but I'll take a shot in the dark and say you are probably getting a null reference exception on your

target

reference, because you are attempting to supply the reference using

FindGameObjectWithTag

.

For this to work, make sure there is only one GameObject in your scene with a tag exactly named like "Player".

 

I mean i wrote this code then I drag its script to my enemy's object , when i run unity for test, enemy doesn't do any thing.
I checked what you said , there is only one game object with "Player" tag

by the way i have this error:
NullReferenceException: Object reference not set to an instance of an object
Enemy.Update () (at Assets/scripts/Enemy/Enemy.cs:25)
for this line:

Code (CSharp):

1.  transform.position = Vector2.MoveTowards(transform.position, target.position, speed * Time.deltaTime);