Authorities in Texas said Friday they have a "person of interest" in the disappearance of a 22-year-old college student last seen more than a week ago.

Investigators said the woman's boyfriend -- whom they did not name -- is "not cooperating" in the search for Zuzu Renee Verk, a student at Sul Ross State University in Alpine, Texas, about 100 miles from the Mexican border. 

The Texas Rangers and FBI are assisting in the search for Verk -- which has expanded outside of the Alpine area -- and a $50,000 reward is being offered for her safe return.

"At this point, we are still believing that she is alive," Alpine Police Chief Russell Scown said, according to Fox affiliate KDFW-TV. "We're hoping for the best outcome. We want to return her safely to her family."

Verk was last heard from during the early morning hours of Oct. 12, according to the Alpine Police Department. Verk's father told local news outlets that she was absent from both school and work later that day.

Verk reportedly left her home for a date at the movies with her on-again, off-again boyfriend on the night of Tuesday, Oct. 11, though police have released few details. 

During a news conference Friday, Verk's family pleaded for her boyfriend to help in the search and cooperate with investigators.

"If you love Zuzu as much as you say you do, and have told me over and over, you will come down here and you will help the police bring my sister home," said Verk's brother, Miles, as he fought back tears.

"I'm asking you please to help us," the young woman's father, Glenn, said of the boyfriend, who has reportedly retained an attorney.

"I haven't seen you yet. I've seen a lot of people here helping," Glenn Verk said. "If you would please come and cooperate with the police department and help us and help them I know that you love her -- I hope that you do. And this would be a way to show it."

The Alpine Police Department said it is looking for two vehicles possibly related to Verk's disappearance: a grey 2006 Jeep Liberty and a 2004 Mazda Miata convertible with a beige top. Both vehicles, police said, were seen in the area between 12 a.m. and 10:00 am on Wednesday, Oct. 12.

The Brewster County Sheriff's Office has also asked area ranchers to inspect their property for "any suspicious signs of disturbed earth, personal items on the ground, anything that might raise your suspicions that it may need to be investigated further."

Verk is described as 5 feet tall, weighing 110 pounds with blonde hair and hazel eyes.

Alpine is about 200 miles southeast of El Paso. Anyone with information on the case is urged to call the Alpine Police Department at 432-837-3486.

FoxNews.com's Cristina Corbin contributed to this report.