How do I adpot my little girl from previous relationship , without her biological father's were abouts ?

You have to track him down. Your going to have to search high and low for him and also prove it to the courts. Isn't he on child support ?

I'm confused. Are you the mother or step mother? If you are the step mother, where is the bio mother?

More details, like your marital status, area you live in, whereabouts off both bio parents etc are needed.