I would have to agree with everything the people above said. Here are a few of my suggestions
1) Advertise creatively. For example, this year, we made some funny posters and put them all around school (girls bathroom would be a good spot, but you would of course, want a girl on the team to put them in there,
)
2) Make a video or hand out explaining what robotics actually is. This year we made a humorous video called "10 Common misconceptions about the robotics team" It was a hit.
3) After your creative recruitment efforts, bring girls who show up to meetings on the team to your workshop, and then ask them to use the power tools (with help/instructions/proper safety of course, at first). I remember being so scared to use the bench saw, but after I did I felt like I had just constructed a 3 story mansion. Using a power tool is quite empowering, no matter what gender you are.
Hope this helps; good luck!