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Two digital-age forms of communication are the focus of a police investigation into the mysterious disappearance of a 43-year-old hiker in Hawaii who relatives believe was the victim of foul play.

Maui police say the active search for 43-year-old Laura Vogel has been suspended until new evidence is found, but relatives believe "something went desperately wrong."

Vogel, a freelance tutor and avid camper, was last heard from on Feb. 21 when she sent a text message to a friend indicating she was "meeting all the locals" in an area known as the birthing pools in Haiku, in Maui County.

Vogel’s friends found her van near the Pauwela lighthouse on Feb. 22. Her keys were inside, which was not unusual, but her cell phone and wallet were missing, said Lt. John Jakubczak of the Maui Police Department. A day later, the back portion of a cell phone believed to be Vogel’s was found nearby.

Tracking dogs hunted fruitlessly for four days along the coastline, and no evidence of foul play or signs of an accident were found during searches of areas that covered heavy vegetation and rocky cliffs. Now, Jakubczak said, search efforts will remain suspended until there is new information.

“What we’re saying is, it’s very suspicious,” he said. “But again, we’re not listing it as foul play because there’s no evidence of foul play at this moment.”

Jakubczak said two calls were made from Vogel’s phone on the night she vanished, including one to a number not previously called on that line. And, he said, the man to whom the number was registered had not been using the line for nearly 10 years. He said the unidentified man is a "person of interest" in the case.

"[But] there’s nothing to say that this person was involved in this," Jakubczak told FoxNews.com. "There are other people who we are continuing to look at as people of interest."

The missing woman's brother, Tim Vogel, of Jupiter, Fla., was among relatives who arrived in Maui to assist in search efforts. He told the Maui News that he’s pleased with the steps officials have taken, but Vogel still believes "foul play" led to the disappearance of his sister.

"Something went desperately wrong," he told the newspaper. "This is not a camper who goes off into the woods and is missing. She is more experienced than most backpackers. She doesn’t just go missing. It’s under very suspicious terms, and we’re very concerned."

He said friends began searching for his sister the day after she vanished, when she failed to show up for a tutoring appointment.

“Her friends started calling because Laura always arrives,” he told The Maui News, “and she’s always on time.”

A Facebook page dedicated to locating Vogel had more than 1,800 fans as of Tuesday morning, many of whom praised her passion for all things outdoors and for being an "independent and free" spirit.

"She always had a smile on her face and a crazy scheme to keep us inspired, strong and alive," one message read. "Laura, I will never forget our backpacking and hiking adventures ... or the many other adventures you took us on."

Vogel’s friends continued search efforts on Monday, according to another post, including patrols of "steep areas" by helicopter, rough waters by Jet Ski and cliffs via rappelling.

"Others doggedly continue the arduous foot-searching in incredibl[y] rough terrain," the post read. "No new signs of Laura, but no one is giving up."

Jessica Vogel said her sister-in-law worked for many years as a high school teacher in New Mexico and has a master’s degree in wildlife ecology. Relatives "pretty firmly" believe Vogel did not just disappear, she said.

"We know that she was with people the night she disappeared and we have yet to hear from those people, which is extremely suspicious to us," Jessica Vogel said. "We’ve been searching and searching. If she had a hiking accident, we would’ve found her."

Laura Vogel is described as 5 feet 8 inches tall, roughly 140 pounds with blond hair and blue eyes. Anyone with information regarding her whereabouts is asked to call the Maui Police Department at (808) 244-6245.