The woman told police she believes she was sexually assaulted.
Police suspect the punch contained some sort intoxicant.
Cameron Kay, president of the USC chapter of Lambda Chi Alpha, has not commented on the investigation, but USC officials have issued a campus crime alert.
"USC takes sexual assaults very seriously and is fully cooperating with the LAPD on the investigation," Michael L. Jackson, USC Vice President of Student Affairs, said in a statement. "We are reaching out to the students and providing as much help as possible. We are also conducting our own investigation into student conduct issues and have placed the Lambda Chi Alpha fraternity on interim suspension until all the facts are known."
LAPD investigators say they have talked to one apparent victim and they are looking into whether or not there could be others.
"She's the only one that has been reported at this time," said Cremins. "We're certainly entertaining the possibility there may have been other victims and that's why we're appealing to the public, that if you were at this party and you saw anything that was consistent with the sexual assault, or if you yourself were sexually assaulted, we need to get your information and to come forward."
Detectives say anyone who can help with the investigation should call (877) LAPD 24-7, (877-527-3247).
MORE LOCAL HEADLINES FROM LOS ANGELES
SEND TIP || REPORT TYPO || TWEET @abc7 || WIDGET