Sizemore, 49, who's been interviewed by detectives and has been cooperative, is not a suspect in the missing-person case, LAPD Det. Carmine Sasso tells PEOPLE.
Actress Megan Lacy Wren, 25, was last seen in the downtown L.A. area on March 31. Although some have described her as his girlfriend, Sizemore told Det. Sasso that she was just a friend, while the actor's manager outright dismisses any claims of a romantic involvement between the two.
The woman's father, Bill Wren, told CBS News that his daughter had been working for the actor as his assistant. Sizemore "indicated that he didn’t know where she was," Bill Wren said.
The Wren family "is very concerned about Megan's unexplained disappearance, especially given the fact that she has a serious medical condition and is in need of medical care," according to a police statement.
Bill Wren added that his daughter has struggled with substance abuse and was recently hospitalized for a serious staph infection. A police handout with various photos of Megan included several of her mugshots from prior arrests.
Sizemore, who's battled drug addiction for years, was convicted of assaulting girlfriend Heidi Fleiss in 2003 and has since been in and out of jail on various drug-related offenses. Last year, the actor was a cast member on Celebrity Rehab with Dr. Drew.
Megan Wren is described as a Caucasian female with brown hair, brown eyes, 5'1" tall, weighing 110 lbs., with a slim build and light complexion.
'Tom Has Nothing to Hide'Speaking to PEOPLE, Sizemore's manager, Charles Lago, said, "Tom has nothing to hide. They were not romantically involved. She was not his assistant and didn't live at his place, either. Megan could've never been his assistant, it's too demanding a job, and she was getting progressively worse due to heroin addiction over the last 18 months."
Were Sizemore and Wren romantically involved? "No," said Lago, who added, "Tom's been clean and sober for two years, and he knows what it's like to struggle with addiction. He'd been trying to help her." Furthermore, said the manager, "Tom's very concerned, and he's in touch with Megan's family on a regular basis."
The acquaintance between the two of them started when "Megan met Tom in the hallway of his building because her aunt lived three doors down from him and they became friends," said Lago.
"I used to kick Megan out of his apartment every time I saw her," Lago continued. "I'm his manager, and my job is to look out for Tom's welfare. He's a very generous guy, so he was trying to help her. I would say to him, 'Tom, she needs to leave.' "
But that wasn't the case. "She would often go to his apartment to hang out, she knew he was a friend, he would let her hang out in his apartment here and there," Lago said.
As for Sizemore's theory on what might have happened to Wren, the manager said, "He has no idea. Friends in that building said Megan disappeared all the time. Tom's too busy to have kept tabs on her, he's constantly working on film shoots."