encourage him to play with them introduce him to them and bring cousins and make them play and once he gets use to them he wont be afraid any more.

Hi adcriv, I can see why you're worried that kindergarten might be an anxiety-ridden, stressful experience for your son and I sympathize completely. The truth is all of us experience some amount of anxiety and tension in new situations and we deal with it in different ways. We tend to notice the extroverts more and associate them with success, but each child is special in their own way. As a parent, you can help reassure your son that he's fine just the way he is.

Talk to your son's kindergarten teacher and make him/her aware of the problem, so that (s)he can make an extra effort to help him adjust. You can also help ease his fear of being around new people by scheduling play dates, where he can spend time with another child one-on-one. Most of all give him a lot of reassurance and affection and listen to his fears.

Education.com has a ton of information on shyness: http://www.education.com/topic/anxiety-shyness/ and I found these articles in particular to be very interesting. I hope they help:
http://www.education.com/magazine/article/Encouraging_Shy_Preschooler/
http://www.education.com/reference/article/Ref_Encouraging_Shy/
http://www.education.com/magazine/article/Ed_Pushing_Your_Shy/

Thank you for the great suggestions and info.

You might want to use a picture book as a vehicle to get him talking about his fears. Although not specifically about social anxiety, "Harry the Happy Caterpillar Grows: Helping Children Adjust to Change" might be a good choice.The story centers on Harry,a caterpillar that has a fantastic life full of games, friends, school and leaf eating. He is stunned when, one day at caterpillar school, he learns that he is expected to  build a chrysalis and become a butterfly. Harry vows to remain a caterpillar forever, as his friends build their chrysalises and move on.  Eventually, Harry  learns to accept change as a necessary part of life, and  joins his friends as a butterfly. There are tips in the back of the book to help parents and educators use the story as a vehicle to help kids talk about their fears, and teach them coping strategies to manage their anxiety.