The sister of missing Fairfax County firefighter Nicole Mittendorff says the family has not been able to gain access to her cellphone data, which they say could help lead to her.

WASHINGTON — Fairfax County firefighter Nicole Clardy Mittendorff called in sick for her last shift before it was reported she was missing, fire officials said Wednesday.

Fairfax County fire officials told reporters Mittendorff telephoned to say she was ill last Wednesday. A text message with her father at 10:50 a.m. that day is the last known communication from the 31-year-old Woodbridge woman.

Meanwhile, Mittendorff’s sister says authorities now have information from her sister’s cellphone account, which she hopes could lead to the Fairfax County firefighter.

Jennifer Clardy Chalmers says Mittendorff downloaded several files to her cellphone shortly before she disappeared. Chalmers wonders whether the files could be maps, which could provide insight into where her sister was heading.

Early Wednesday, Mittendorff’s wireless carrier, citing federal law, wouldn’t provide information on the data, even though Mittendorff’s father owns the account, according to Chalmers.

She declined to name the wireless carrier.

Nicole Mittendorff was reported missing Friday, when she failed to show up for work. Her car was found Saturday night in a remote parking lot in Shenandoah National Park.

Virginia State Police have said there is no evidence of anything suspicious in Mittendorff’s disappearance, and even with the passage of a week, this remains a missing-person case.

Since Mittendorff’s disappearance is not considered a criminal matter, law enforcement cannot subpoena cellphone records.

Wednesday morning, on the Find Nicole Now Facebook page, administered by Chalmers and her family, the family asked for help from an attorney with telecommunications expertise who could help gain access to the data.

By Wednesday afternoon, the situation had changed — Chalmers said “the information is now with the authorities.”

Chalmers would not describe how the information was gathered.

Virginia State Police spokeswoman Corinne Geller has not said whether anything found in Mittendorff’s cream-colored Mini Cooper would indicate where she was heading, or what could have happened to her.

State police have fielded more than 100 tips from the public since the weekend, Virginia State Police said Wednesday. Search efforts were set to resume at daybreak Thursday.

Five trails in the Whiteoak Canyon area remain closed for the search, according to the National Park Service.

Anyone with information about Mittendorff’s whereabouts can call the Virginia State Police at 703-803-0026 or send an email to questions@vsp.virginia.gov.