It's a parent's worst nightmare: discovering their child disappeared overnight, gone without a trace.

That's what happened to Heather Simmers-Bond, whose son Devin went missing two years ago, seemingly into thin air.

So what happened to Devin? No one knows. Although the case remains open and active, and investigators still receive tips and leads, no clues have pointed to where the now 18-year-old is.

“(Detective Will) Pinson is actively working Devin’s disappearance to find answers, especially for Devin’s mother and his family,” Rutherford County Sheriff's Office spokeswoman Lisa Marchesoni said. “We hope people who know something will call Pinson at 615-904-3056.”

March 30: Hours before Devin disappears

It was a regular day. Devin was on spring break from Riverdale High School, where he was a freshman. He'd just turned 16, and like most teen boys, his life revolved around playing video games and scarfing down his favorite foods. In his case, he couldn't get enough of Camino Real's queso dip, his mom said.

Simmers-Bond got home from work around 6:30 p.m. and ate dinner with her family. She had no suspicion that it was the last family dinner for a while.

With a laugh, she recalled how Devin ate an unusual amount of food that night. He couldn't stave off his hunger, she said.

Around 11:30 p.m., Simmers-Bond decided to head to bed. It was late, and she was tired. She ducked into Devin's room to wish him a goodnight. He was playing video games, as he usually did.

"I'm going to bed," she told him. "Don't stay up late. I love you."

That was the last time she saw Devin or heard his voice.

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March 31: A frantic phone call

Around 10:30 a.m. March 31, 2017, Simmers-Bond's phone rang. It was her husband alerting her that he couldn't find Devin.

Initially, she wasn't too worried, but she still came home from work early and went to a nearby friend's house looking for him.

After arriving home, the panic set in. The mom learned that Devin had stuffed blankets under his sheets to make it look like he was in his bed. Devin's brother Dylan, then 9, discovered the decoy.

Simmers-Bond drove to Devin's ex-girlfriend's house looking for him. After reaching out to her, Simmers-Bond learned the ex-girlfriend had ended things with Devin around 7:30 p.m. the day before.

The couple, who'd been dating only a few months, split amicably. Simmers-Bond said the ex-girlfriend said Devin was "kind of" upset about the breakup.

"I think it was the straw that broke the camel's back," his mother said. "But it's not fair to put all that blame on her."

By 11:30 a.m., 12 hours after seeing their son for the last time, Devin's parents called the police to report him missing.

"It's very surreal, like I can't believe I'm reporting my child missing right now," Simmers-Bond said.

At first, dispatch didn't seem concerned. It issued a BOLO for Devin and wrote down the parents' complaint, but that was it.

It wasn't until friends and family members put pressure on the Rutherford County Sheriff's Office that it took the complaint more seriously, Simmers-Bond said.

Although the mom said she doesn't think the sheriff's office acted aggressively enough at first, she's pleased and grateful with the investigation's progress since then.

The deputies brought out tracking dogs to trace Devin's scent. A dog caught a whiff and took investigators out the front door. In retrospect, Simmers-Bond thinks the dog picked up the wrong scent.

The family had surveillance cameras set up, and although video footage didn't capture Devin leaving, it showed a light in the backyard for about 15 minutes in the middle of the night. They think that's when Devin left, skipping out through the backdoor.

4:56 a.m. March 31: The last trace of Devin

Deputies pinged the teen's phone. Judging by data collected from a nearby cellphone tower, investigators placed Devin near Barfield Crescent Road between 4:56 a.m. and 5:30 a.m., his mom said. During this time, a tipster reported a possible sighting of Devin: They'd seen a teen walking on that road who matched Devin's description.

He wasn't seen again.

His phone was turned off after the ping picked up by the Tiger Hill cellphone tower. There hasn't been any cellphone activity since.

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So what happened?

Simmers-Bond said she and the investigators believe Devin left on his own. Video surveillance doesn't show anyone picking Devin up from their home, and based on the ping activity from the teen's phone, investigators believe he walked rather than drove.

Detectives thoroughly searched Devin's room. They touched every item the teen had, combing for clues. They even pulled posters and photos off the walls and looked behind them, his mom recalled.

Although investigators were able to trace cellphone activity to pinpoint where Devin was, that's all they could gather from the teen's cellphone use.

Devin, like most teens, liked to text. He wasn't big on social media, his mom said, but he was constantly communicating with friends. The problem puzzling investigators now is the way he texted: It wasn't through a traditional messaging service. Instead, Devin used Kik, a messaging app that doesn't store messages, so detectives aren't sure who Devin was talking to in the hours leading up to his disappearance.

After her son vanished, Simmers-Bond discovered one of her husband's guns was missing, along with a jacket, a drawstring bag and a few pairs of pants. It appeared that he was planning to skip town.

"I think he is (alive)," his mom said.

"I'm more aware than anybody of the possibilities," she added, a nod to the prospect that Devin may, in fact, not be alive. But that doesn't diminish her hope that she'll see him again.

Looking for Devin: 2 years later

Although Bond family members have ceased on-foot searches, they haven't stopped looking for their son through efforts online. They've created various social media pages to keep people informed of their search, and they still receive tips on his disappearance.

They hand out flyers and decals and try their best to keep Devin's name alive. Simmers-Bond said her biggest fear is that people will forget about her son.

Although she hasn't seen him in two years, that doesn't stop her heart from lifting when she's in public and catches a glimpse of a lanky blond teen. Even though she said she knows it's not him, she can't stop herself from stealing a second hopeful glance.

"I have to know what happened to him," she said.

Until that day comes, she finds faith by helping others in similar situations. Unfortunately, Simmers-Bond has company when it comes to missing children: It's estimated that nearly 460,000 children disappear annually in the United States.

It's a club that no one wants to join, but many do. Just as parents of missing children helped her carry the burden of losing Devin, so she now does for other parents.

"Not many people understand this," Simmers-Bond said.

Follow "Bring Devin Home" on Facebook to stay updated on the search for the missing teen.

Reach Brinley Hineman at bhineman@gannett.com and on Twitter @brinleyhineman.

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