A 33-year-old Missouri mother heading to her son's birthday party never showed up, police say.

Amy Oberhaus was last seen by her family at a bowling alley in St. Peters, Mo., on July 31. Oberhaus left to visit friends at a home in Dellwood, Mo.

Oberhaus left the friends' home around 8:30 p.m. to head to her son's birthday party in St. Peters, about 28 miles west of St. Louis, but she never arrived. She was last heard from at 9:16 p.m. on July 31.

“It appears to be out of character,” Brad Norris, a spokesman for the St. Peters Police Department told FOXNews.com. “She’s never been gone this long.”

Police have no suspects and haven’t received many calls with leads, Norris said.

“We haven’t ruled out anything,” Norris added.

Oberhaus, of Lincoln County, has no criminal background and is not married. She has an 11-year-old son and a 13-year-old son.

The white female is 5 feet, 11 inches with blonde hair and blue eyes, and has a tattoo of a flower on her left ankle. She has a medium build and weighs 160 pounds.

She was last seen wearing a light-colored T-shirt, blue jean shorts, white tennis shoes and white socks.Oberhaus was driving her 2006 black Jeep Commander with Missouri license plates 0AH-28Z.

Police ask anyone with information to call the department at 636-278-2244, ext. 520, or Crime Stoppers at 636-278-1000.