Veronica "Nikki" Ruiz, 25, a criminal investigator for the IRS, is missing in the mountains outside of Mill Valley, California.

Ruiz, a resident of Mill Valley, was last seen on Monday, December 3. It is believed she was sighted Monday morning at the Blithedale Trail entrance at Mt. Tamalpais and an hour later at the nearby West Point Inn. Family members and friends report that she told several people she was planning on hiking near Mt. Tamalpais last Monday.

Mill Valley Police are handling the case with help from the FBI, but as of this past weekend, the official search had been suspended. More than 100 family members, friends, fellow IRS investigators, and other volunteers continue the attempt to locate Ruiz.

"All of her friends have tatken off of work (to search Mt. Tamalpais). I think we are all trying to be optimistic. It's just devastating," said Brina Amata, a friend of Ruiz.

Authorities have indicated that Ruiz is likely to be armed, since IRS criminal agents are required to have access to their firearms at all times.

Ruiz's car is still at her house, located near the base of Mt. Tamalpais. It has been determined that her backpack, her firearm, and running gear are missing from her home. A backpack that was discovered in a Northern California state park will be examined to determine if it belongs to Ruiz.

Latest update: What was believed to be a backpack that might have belonged to the missing IRS agent turned out to be a pile of leaves. The search is expected to continue during the weekend of December 15-16.

Ruiz works for the San Rafael office of the Internal Revenue Service, is a graduate of the University of California at Berkeley, and worked at the tax and audit firm KPMG before joining the federal tax agency, according to The San Francisco Chronicle.

Ruiz's family and friends have created a Web site where people with tips or questions can communicate their information.

Ruiz is 5 feet 5 inches tall and weights 120 pounds. She was reported missing after calling in sick at work last Monday, the 3rd. A friend who asked Ruiz to join her for lunch that day reports that Ruiz declined, indicating she was going hiking. Ruiz was apparently despondant over a breakup with her boyfriend the previous weekend. Anyone with information regarding the disappearance is instructed to contact the Mill Valley police at 415-389-4100.