Trying to find my half sister.

Hi. I'm new to the forums. I just thought I'd give it a try. I had just typed a fair bit about this here, but I decided to delete and start over, because I probably would of confused you. I was confusing myself. Anyway, I learned I had a sister from my father's side around two years ago, but probably no longer than two years. I can't be sure of the time range. My grandma passed away last year. My mom and I went down for her funeral. We were going through her things-- just gathering stuff; pictures, etc. And we found a picture of my sister. It was the first time I had even seen a picture of her. She was only 10 months in it. I had lost the picture a few months later when we were packing up things to move. Recently, I found it when I was going through boxes. I just had a son born last year in December; he just turned 7 months yesterday. What really intrigued me to start searching for my sister was him. Again, she's only 10 months in the picture; on easter day with a easter basket-- "first easter 1982". She looks so much like my kid, though. They almost look like identical twins. All I know about my sister is that she was abandoned real young, I'd guess she was still a baby up until 5 years old, by her birth mother at a baby sitter's place. And that the baby sitter adopted her. She was born in Charleston, South Carolina. Candice Canady was her name tooken when she was adopted. And that she was born around June 1981. I've tryed adoption registries; both her name tooken when she was adopted and her original birth name, and I've found nothing there. I've tryed white pages and have actually called a few random people in South Carolina, such as "C P Canady" etc, asking "Is Candice there?", and have gotten no where. I emailed a few businesses that deal with finding people; one couldn't do it without a birth date, and another had found someone but I was needed to pay $150 first. I had asked the latter to confirm her birth father's name and then I would gladly pay, but they never emailed back so I got nothing from them, either. I haven't done much yet, or tryed everything-- put much time into it, because I just recently started trying to find her. I don't know where to start, though. Her adopted name could easily of been changed by now, and my-- her original last name may of never tooken affect with her; my dad may not of been present at her birth and she took her mother's name. So I'm just kind of lost. It's very stressing and time consuming. Any information I know about her is all from my mother. I never knew my dad; he died when I was two years old. And I don't know anyone from my father's side of the family at all. Is that where I should start?? Trying to find someone from my dad's side and going from there? It seems like nothing else would work because of the little information I can provide about my sister. Please respond if you can help any, or give me a starting point. Thanks for reading.Sorry if this is the wrong section to post. I thought I was in the right section but I wasn't signed in, or it timed out while I was typing, and I had to start over. I wasn't sure what section I was in at first.