"This is highly out of character for them and after extensive searching and investigation Sunday afternoon and evening, no clues have been located," the sheriff's news release stated.

The office reported that Carol Kiparsky, 77, and Ian Irwin, 72, were last seen on Friday at a rented vacation cottage on Via De La Vista in the Inverness/Seahaven community, near the coast of Tomales Bay. They were due to check out Saturday morning but all of their belongings, including phone, wallets and vehicle, were left at the cottage. They had also missed an appointment on Sunday, the sheriff reported.

A Palo Alto couple who had rented a room in Marin County last week and were due to check out Saturday morning have gone missing, prompting a search-and-rescue operation that stretched into Wednesday, according to the Marin County Sheriff's Office.

More than 60 searchers from local, regional and state agencies are assisting the Marin County Sheriff's Office in locating a Palo Alto couple last seen on Feb. 14. Image courtesy Marin County Sheriff's Office.

Palo Alto residents Carol Kiparsky and Ian Irwin were last seen at a rented vacation cottage on Via De La Vista, highlighted above in black, a street in the Marin County community of Inverness/Seahaven, on Feb. 14. Image courtesy Google Maps.

Neighbor Connie Cotton said that Irwin and Kiparsky are an active couple who enjoy hiking and walking. "He's been working on a project in his backyard recently," she said, adding that she does not view them as "elderly."

Kiparsky was described as Caucasian, 5 feet and 2 inches tall and 115 pounds with gray hair and blue eyes. Irwin was described as Caucasian, 6 feet and 1 inch tall, 175 pounds and bald with some gray hair and blue eyes.

Wednesday's search took along the water's edge in Inverness with assistance from a dive rescue team, a K9 team and Point Reyes National Seashore employees, according to the sheriff's office. The group used a remotely operated vessel and side scan sonar as part of the operation.

The search for the couple continued on Monday by land and air with a total of 136 search-and-rescue members from throughout the Bay Area, according to a tweet from the sheriff's office. The effort resumed Tuesday with 40 people, including K9 teams, unmanned aerial vehicles, boat crews and ground searchers, according to the sheriff's office.

About 60 searchers from various agencies, including the Marin County Sheriff's Office, Marin County Search and Rescue, Inverness fire department, the California Highway Patrol, California State Parks, Marin County Fire Department and National Park Service investigated the disappearance throughout Sunday but could not locate the couple, according to the sheriff's office.

Anyone who has seen either Kiparsky or Irwin any time since Thursday is asked to contact the Marin County Sheriff's Office at 415-479-2311.

Just days after the Palo Alto couple was reported missing, the Marin County Sheriff's Office announced it was also searching for a 76-year-old Robert Bennett who was last seen Monday afternoon around Valley Stone Trail Head in Big Rock Ridge, just about 25 miles away from the Palo Alto couple's last known location. He was found late Tuesday night at an undisclosed location and taken to a hospital where he was reunited with his family. The cases don't appear to be related.

Massive search underway for Palo Alto couple, missing since Friday

Search and rescue operation in progress for Carol Kiparsky and Ian Irwin