Yes human beings do live in karachi, but lets be realistic. Karachi is not a city you should go alone in - whether you are a guy or girl- EXPECIALLY if you've never been there before. The original poster has never even to Pakistan before!!
I love Karachi a LOT, but it is very very different. Yes human beings live there, but as w/any nation there are bad human beings in this world. Karachi does not have a Police system, so calling for help is not as easy as you many think , and you can easily get lost in a city that for the most part does not have street names even. Karachi, unfortunatly, is submerged in a poverty that you can't understand until you actually go there. Though povery brings out many good in many people, it also unfortunalty brings out the worst of the worst.
I would suggest that atleast for the first visit go there with someone. Karachi is very different from the first world countries that you are used too. No TV or movie can show you the huge difference. I strongly suggest you go with someone when you make your first visit there.
It is indeed any eye opener to how most of the world lives, and more likely you will be forever grateful, for what Allah has given you! Best of luck!