Seeder command not working Laravel 5.4

I am new to laravel I am trying to follow a tutorial in which I create a Database Seeder for the DB. So for that, I have used php artisan make:seeder ArticlesTableSeeder command

Seeder

class ArticlesTableSeeder extends Seeder
{
    public function run()
    {
        // Let's truncate our existing records to start from scratch.
        Article::truncate();

        $faker = \Faker\Factory::create();

        // And now, let's create a few articles in our database:
        for ($i = 0; $i < 50; $i++) {
            Article::create([
                'title' => $faker->sentence,
                'body' => $faker->paragraph,
            ]);
        }
    }
}

Now, when I run the php artisan db:seed --class=ArticlesTableSeeder command I have got this error

[Symfony\Component\Debug\Exception\FatalThrowableError] Class 'Article' not found

I do have a article modal

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Article extends Model
{
   protected $fillable = ['title', 'body'];
}

What am I doing wrong here ? I have searched for this error and found the maximum of them are due to spelling mistakes. I think I don't have a spelling mistake here. What is wrong with this code ?

Help would be appreciated.