我们用QQ及微信的时候，常说说加某人为好友。我见到过以下这些说话，因为都是出自英语不怎么好的中国人之口，所以，我感觉不是太地道：

Why did you add me? 

You can add me. 

You can add me as your friend.

You can add me into your friend. 

You can add me to your friends.

You can add me to the list of your friends. 

You can add me to the list of your QQ contacts. 

You can friend me by QQ. 

大家感觉以上哪些说法正确，哪些错误。要怎么正确且简单表达？