Erro ao setar "Persistence.createEntityManagerFactory"

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.annotations.Version).
 log4j:WARN Please initialize the log4j system properly.

package entities;
 
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
 
@Entity
@Table(name="people")
@NamedQuery(name="getListOfPeople", query="select p from Person p")
public class Person {
 
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer id;
    private String name;
    private String address;
    private String city;
    
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAddress() {
		return address;
	}

 
	public void setAddress(String address) {
		this.address = address;
	}
	public String getCity() {
		return city;
	}
	public void setCity(String city) {
		this.city = city;
	}
        
}

package services;

import java.util.List;
import javax.persistence.EntityManager;
import entities.Person;

public class PersonService {

    private EntityManager em;
    /**
     * Constructor
     */
    public PersonService(EntityManager em) {
        this.em = em;
    }
 
    public void persistPerson(Person person) {
    	
        em.getTransaction().begin();
        
        try {
        	
            em.persist(person);
            em.getTransaction().commit();
            
            System.out.println("Person has been inserted successfully");
            
        } catch (RuntimeException re) {
        	
            System.err.println("Error inserting the person...\n" + re.getStackTrace());
            
            em.getTransaction().rollback();
        }
    }
 
    @SuppressWarnings("unchecked")
    public List getListOfPeople() {
    	
        return em.createNamedQuery("getListOfPeople").getResultList();
    }
}

package services;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class PersonServiceFactory {

    public static PersonService create() {
    	
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("jpa_intro");
        EntityManager em = emf.createEntityManager();
        PersonService personService = new PersonService(em);
        
        return personService;
    }
}

package introduction;

import services.PersonService;
import services.PersonServiceFactory;
import entities.Person;

public class MainClass {
	
    private Person person;
    private PersonService personService;
 
    public static void main(String args[]) {
    	
        MainClass main = new MainClass();
        
        main.insert();
}

    /**
     * Default Constructor
     */
    public MainClass() {
    	
        personService = PersonServiceFactory.create();
    }

    private void insert( ) {

        person = new Person();

        person.setName( "TESTE" );
        person.setAddress( "AQ TESTE" );
        person.setCity( "SANTA CATARINA" );
        
        personService.persistPerson( person );
    }
}