try Bach Flower Essences. They are amazing and help people a nd animals with out harm . Mimmulus might be a good one, it's for fear.

I too had a very shy kitty, although she was fine with me. I started rewarding her for even the smallest amount of social behavior. She's not big into treats or food, but she loves to be made a fuss over and told what a good kitty she is. I encouraged other family memebers to carry her around and show her interesting things, not letting her down until she relaxed. When they did put her down, they would give her lots of praise and pets on the head. She has gotten much better. She is still very shy with strangers, but at least will now actively seek attention from family members. Like changing any other behavior in a cat this took a long time, 3 years! Socializing a shy cat takes a lot of patience. Good luck with your kitty.