Remember: your goal is not to get people to meetings, it is to get people INVOLVED.
My suggestion would be to contact those 12 parents...you did take attendance, didn't you...and start with them.
Have specific ideas what you want to ask them to do, but first ask them if they have specific ideas what they want to do. Have ideas both for opportunities to raise funds and spend funds. Don't directly ask anybody to take on a major project by themselves, but leave the door open for them to volunteer.
Last year our school had no PTO at all. The year before we had a part time principal. Now we have a EXCELLENT principal and I got volunteered to be the PTO pres. We have had 2 meetings. The first meeting I set for during Parent-Teacher conferences and we had about 12 parents so up. More than the principal and I ever dreamed. LOL The second meeting no one showed. I have no clue what I am even suppose to be doing. I want to do certian things for the kids like setting up a a RIF program. I have ideas for fundraisers but I am only one person and can't do it all by myself.... even if I wanted too.I don't know where or how to begin. I need a mentor. Heck I've never even been to a PTA/PTO meeting before. HELP ME. Please.