The fastest way to become comfortable singing in front of others is to do so - often and over a long period of time.
If it helps to have someone else singing instead of you doing a solo, sing with others in your band, then gradually have the others cut back on how loudly or how much they sing. Try singing as an echo of what someone else sang or what the whole group sang for another low-key type of solo experience.
Practice singing for family, friends, neighbors, classmates, any and all gatherings you can possibly find where you know that the audience is going to be friendly and supportive. Remind yourself that you are brave and confident enough to get up and share your love of music with others; tell yourself that those listening are enjoying your performance and wishing they had the nerve to do the same but don't; imagine the audience in their pajamas to make them less threatening; ignore the audience and sing to a spot on the back wall over their heads - find the trick(s) that work to help you and go for it!