A South Florida mother is asking for help to find her missing 28-year-old daughter, who hasn't been seen or heard from in almost a week.

Gena Sims' family believes she returned to South Florida from a trip to Houston last Friday. They said Spirit Airlines told them Sims boarded and then landed at Miami International Airport. Since then, they said her phone has gone straight to voicemail and she has not responded to any calls or text messages.

According to her Instagram page, Sims founded the Autism Theater Project because her younger sister, Olivia, is on the spectrum. Sims also helps care for the 20-year-old as a home health nurse.

"Hi, my name is Gena Sims, and I run the Autism Theater Project," Sims started a video shared on her Instagram last month.

Family members told CBS News Miami that the project, along with her music and helping to care for her younger sister, are major parts of Sims' life. There's been no activity on her social media since her disappearance.

Her mother, Christine Sims, said her daughter is normally busy but reliably responsive.

"Well, she's very, very preoccupied and busy," she told CBS News Miami. "She's a very busy person, a very hard worker, very dedicated to what she's up to, but I reach out to her, she's gonna respond. It may not happen right away, but she's definitely gonna respond and usually it's pretty quick."

The family shared a screenshot with CBS News Miami of what they say was the last text message sent from Sims' phone.

The thread starts with a message sent from her mom at 9:26 p.m., reminding her to call her grandmother. A response comes at 11:44 p.m., saying, "Hi, I had a change of plans. I'll be addressing an emergency."

That is the last message from the phone. Questions inquiring about the emergency have gone unanswered. Sims' voicemail is now full.

Her mother told CBS News Miami that she is worried.

"I'm concerned that her phone seems to be missing, that somebody had texted something on her phone Friday night that was not her. It was not sounding like her and it's been a week almost," Christine Sims said. "This is crazy."

According to her social media pages, Sims attended New World School of the Arts and went on to attend Carnegie Mellon University. In addition to her work with the Autism Theater Project, Sims is also known in the community as a singer performing at local gigs.

Her family is desperate for answers and is urging anyone who may have seen Sims or knows where she might be to come forward.

Her mother sends this message to her daughter:

"Gena, this isn't like you. I'm not sure what's going on, but you need to reach out to me, not through your friends, not through social media or you know. I understand I haven't seen anything in that realm but you need to reach out to me, I'm your mother. Me and your sister are waiting for you to come home."

Anyone with information on Gena Sims' whereabouts is urged to contact the Miami-Dade Sheriff's Office immediately.