Faceniff is probably the most easiest way to gain access to someone’s  Facebook account and also works for twitter, YouTube, amazon, and  blogger accounts. It can be done completely from your android phone and  is compatible with most of the android devices.

Note: It won’t work, if the person is using https security option in Facebook.

What this requires:

• Your android phone must be rooted/unlocked.
• You must be on the same network as the person you want to hack into.
• The person must be currently using Facebook on any device

Once you have unlocked/rooted phone, you need to download the .apk file from here http://faceniff.ponury.net/ It’s free for the first three accounts you get into after that you have to pay a certain amount. You can download the cracked version here.

Once the app is downloaded, install it and then connect to the Wi-Fi of your victim.

Open the faceNiff app and press the start button on the top. If it ask you to allow permission for the app, do so.

It will now be monitoring activity. Anyone who uses Facebook,
YouTube, twitter, amazon on the network you are connected to will show
up on your phone. Simply click on them and you will be logged in into
their account.

Note: It might take 2-3 minutes to load up the screen. So have patience.

If nothing is showing up, try using stealth method in FaceNiff. Some
rooters prevent these kinds of hacks; stealth method will attempt to
bypass this.