Kelly Rothwell was supposed to graduate from a St. Petersburg College police academy on Wednesday night.
Instead, her family and friends gathered outside the college's Allstate Center and held a candlelight vigil in her honor.
Rothwell went missing one month ago, and no one has seen or heard from her since.
Lindsay Rothwell, Kelly's twin sister, said she has no idea what happened to her.
"We hold onto hope always," Rothwell said. "Because she will come home. Somehow or another, she will come home."
"I just wish that the person that might be responsible for all this would cooperate and talk to help all of us out," Rothwell said.
On March 12, Kelly Rothwell told a close friend over lunch that she was going to break up with her live-in boyfriend David Perry, 46, a former New York state prison guard.
Perry was located by authorities in New York shortly after Rothwell was reported missing. He has refused to answer detectives' questions about Rothwell and has also refused to take a DNA test.
Rothwell, 35, of Indian Rocks Beach was a police academy recruit since November. She had not missed a day until she was reported missing.
Rothwell's mother, Nancy, said in March it was out of character for Rothwell to not contact family or friends for a long time. She said her daughter is a private person, so she didn't share any concerns with her regarding any troubles she may have been having with Perry.
The missing woman's sister said it has been hard.
"Every time you hear a phone call, you think it might be her or knock on the door," Lindsay Rothwell said. "It's heartbreaking."
Anyone with information about the case should contact the Pinellas County Sheriff's Office at (727) 582-6200. To remain anonymous, call Crime Stoppers at 1-800-873-TIPS (8477) or go to www.crimestoppersofpinellas.org.
News Channel 8 reporter Peter Bernard contributed to this report.