I generally don't use one but when I do I definitely prefer the opposite sex as a wingman. Girls are absolutely stellar at helping me get a girl. What about you guys? Do you prefer the opposite sex, same sex or are they both equal in your eyes?
I just tell them when I see a girl I like and at that point she will get more flirty with me and play it up like she is into me. We will dance, have fun, and she will exaggerate everything. Girls tend to get really intrigued by guys that have a girl(s) all over them. I never had them approach the girl for me or anything but I might ask the girl and her friends to come dance with my friend and I. They are usually more willing because they have seen me with a girl so they are more comfortable with the situation. Then my friend can game me up from there by talking about me and eventually I move on the girl I like. By that point I am already in without saying very much. This is just one example though it varies from situation to situation but after I started using girls as wingmen I would never use a guy again.