You should wait for him to be ready because, if you beg him he'll think your desperate so in the mean time try to talk to his friends to convince your boyfriend to hold your hand
Ooh.. My boyfriend used to be shy to hold my hand. It takes time.. Give him time to adjust being with you. Maybe you could hold his hand to show him that you want your hand to be held and that it's ok to touch you. Make him comfortable.
I had this same problem. What you need to do, is probably just go for it yourself. Take his hand, and see how he reacts.