One of the men brandished a gun and both sexually assaulted the victim before stealing money and personal items, police said.
It was only after the men fled - about 5:30 a.m. - that the victim was able to call 9-1-1.
McFadden said a secured main door leads to six apartments in the complex, including the victim's.
"How they got into that main door is still under investigation," he said.
McFadden said police don't believe the assailants picked the apartment complex at random but he said the victim may not have been their intended target.
Authorities canvassed the neighborhood on Monday for surveillance footage to no avail.
The first suspect is described as a 5-foot-11 black man in his mid-20s with a light complexion, thin build, small goatee and various tattoos on his neck.
The second is described as a 5-foot-9 black man in his mid-20s, with a dark complexion, who was bald and clean-shaven.
This is not the first time criminals have struck at St. Ives. In November 2012, a man was fatally shot in the head at the complex. In June 1997, three men - two of whom were brothers - were shot to death in a townhouse at the complex.
Anyone with information on the sexual assault case is asked to call the Special Victims Unit at 215-685-3251.
On Twitter: @FarFarrAway