Sharing to facebook, twitter via share intent android

I am currently trying to share text to gmail, facebook and twitter. I am using share intent method to share. Below is the code i used to share

Intent sharingIntent = new Intent(Intent.ACTION_SEND);
       sharingIntent.setType("plain/text");
       sharingIntent.putExtra(android.content.Intent.EXTRA_TEXT, "My text");
       startActivity(Intent.createChooser(sharingIntent,"Share using"));

The above code only show share options like gmail and skype. Why is facebook and twitter options not shown in the list even though i had the facebook and twitter application installed in my device?