What is wrong in my android app with HttpPost?

I'm making a new android app, when I send a values with HttpPost to my web file post.php, but it is don't working. What is it wrong ?

activity_activity_main.xml

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
xmlns:tools="http://ift.tt/LrGmb4"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".ActivityPrincipal">

</RelativeLayout>

ActivityPrincipal.java

package com.pixelayer.httppost.httppostandroid;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

import android.util.Log;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;


public class ActivityPrincipal extends ActionBarActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_activity_principal);

    HttpClient httpClient = new DefaultHttpClient();

    HttpPost httpPost = new HttpPost("http://ift.tt/1zYSQMa"); //
    replace with
    // your url

    List<NameValuePair> nameValuePair = new ArrayList<NameValuePair>(2);

    nameValuePair.add(new BasicNameValuePair("nome", "test_user"));

    nameValuePair.add(new BasicNameValuePair("site", "testeandroid"));

    // Encoding data

    try {
        httpPost.setEntity(new UrlEncodedFormEntity(nameValuePair));
    } catch (UnsupportedEncodingException e) {
        // log exception
        e.printStackTrace();
    }

    // making request

    try {
        HttpResponse response = httpClient.execute(httpPost);
        // write response to log
        Log.d("Http Post Response:", response.toString());
    } catch (ClientProtocolException e) {
        // Log exception
        e.printStackTrace();
    } catch (IOException e) {
        // Log exception
        e.printStackTrace();
    }

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_activity_principal, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://ift.tt/nIICcg"
package="com.pixelayer.httppost.httppostandroid" >

<uses-permission android:name="android.permission.INTERNET" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".ActivityPrincipal"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest>

Thank you so much