Darrell Broussard, assistant police chief in Cleveland, Texas, said the suspects so far include 13 adults and five juveniles, ages 14-27, CNN reported.
"There have been leads during our investigation that have alerted us to other possible persons of interest," Broussard said. "The investigation is ongoing."
Four students in the city's school district who had been arrested Friday appeared in a Liberty County courtroom Monday and pleaded innocent to charges of aggravated sexual assault of a child under 14, KHOU-TV, Houston, reported.
The charges were brought after the 11-year-old girl reported to her principal that she had been attacked during the Thanksgiving holiday at an abandoned mobile home in Cleveland.
James Evans III, an attorney representing four defendants, told the TV station he had heard there could be "as many as 28 or more" suspects.
"It's a tragic situation, as we all have come to realize. The families are dealing with it -- it's a very stressful environment," Evans said.
More suspects are expected to have court hearings next month.