Q: how can i get my pyrenees to trust people outside of the family?

my 18 month old pyrenees is a wonderful, sweet, big teddy bear...at home, when it is just the family. whenever we go out (ie:on a walk or to the dog park) he becomes wicked fearful of people...loves any other dog he meets, but shys away from people. i would love to get hito be less fearful.