As a chapter founder, I was in a similar situation. When my local became a colony of AEPhi, we had ten members. By the following fall we had 22, enough to be chartered.
Our biggest source of new members was formal fall rush. Is your colony permitted to rush at the same time as the chartered fraternities? If so, rush aggressively during this time. If not, do whatever you are allowed to do to get your name out.
We had an informal spring rush and an informal fall rush. Every sister was required to find at least one unaffiliated freshman or sophomore and invite her.
Use the Pitt house if you can, and ask the brothers if they'll help you out. (They should!)
Above all else, don't just go for numbers. It's much better to have 5 quality new members than 20 people who don't care and who are just in it so they can, say, live off campus and get out of having to buy the school's meal plan.
Good luck!
