xcrunner said:
But what costumes have worked for people in here?
A good approach to get attention is to take a character or series of characters from your childhood and work/play with them. This works especially well if you are in a group of guys coordinating a twist on the same basic outfit, I.e. Sesame street wearing suits, a take on Disney characters from Alladin, the Cookie Monster, four or five or six Waldos (approach girls and ask: "we can't find the seventh one, have you seen him?"), the Lion King, etc.
When this is well done, girls might want to approach you for pictures with them.
Create presence by being/talking in-character in your group, especially as girls walk by. A mask also adds to allure when you establish a presence around them and they don't know what you look like.