Crystal McDowell, 38, was last heard from on Aug. 25, shortly before Hurricane Harvey hit Houston.
Chambers County Sheriff Brian Hawthorne believes foul play may be involved.
McDowell's Mercedes was found partially submerged in floodwater in a Mont Belvieu hotel parking lot. All of her personal belongings had been removed, and investigators don't think she parked it in the spot where it was found.
Authorities said there has been no activity on her credit cards or her passport.
McDowell was last seen wearing a pink and purple dress and driving a new model Black C Class Mercedes.
Family members said she had been living in the Legends Bay subdivision with her ex-husband and two small children, but she had begun to see a new boyfriend.
"She was on top of the world. She said she was the happiest she'd ever been in her entire life," uncle Jeff Walters said.
Anybody with any information about McDowell's whereabouts is asked to call Chambers County Police Department at 409-267-2500.
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