Two Dads, Two Lost Boys and the International Search for Mother Who Vanished with Them Determined, Larry Hummel and Bob Pfeifer took the search into their own hands.

Feb. 28, 2014 -- In Los Angeles, two fathers were living a nightmare. Each of their sons, who they allowed to travel on vacation to Slovakia with their mother, the woman they were both once married to, never returned home.

“We just, we couldn’t locate them or find them,” one of the dads, Larry Hummel, told ABC News’ “20/20.”

For nearly two years, Hummel and the other father, Bob Pfeifer, both wondered where their sons were and if they would ever find the mother who took them.

“She cut off, went dark on her phones, went dark on email,” Pfeifer told “20/20.”

Watch the full story HERE.

Hummel’s son Sasha was just 3 when he last saw him. “It's strange because I feel like I'm with him all the time and he's with me all the time, except he's not here,” Hummel said. Sasha, who was breastfeeding at the time, lived with his mother. Hummel had visitation rights every other weekend and a couple nights during the week.

The last time Pfeifer, who had shared custody, saw his son Jerry, he was 9. “I can’t believe he’s gone,” Pfeifer said. “I see his picture every day.”

Years earlier, during a visit to Prague, Pfeifer first met the boys’ mother, Maria Misejova, a native Slovakian. She told him she was training to join Slovakia’s Olympic team and planning for medical school.

“I was living in Hollywood, and the time filled with the disingenuous,” Pfeifer recalled. “And I thought I met an innocent person.”

A high-level record executive in the 1990’s and a part of the booming video game industry, Pfeifer was ready for a family. As a long-distance relationship bloomed between the two, they eventually married, and Misejova was pregnant within a couple of months.

Misejova moved to Los Angeles but her relationship with Pfeifer soured even before the baby arrived. By the time their son Jerry was born, Pfeifer had already filed for divorce. The two took to court to battling over custody of their son.

“It was contentious, but we always … I was very much involved in my son’s life,” Pfeifer said.

During the course of those legal struggles, Pfeifer also found himself facing charges and pleading to a felony in a high profile wire-tapping case. He ended up cooperating with the prosecution, and later, judges decided his past should not get in the way of custody of his son.

During their custody procedures, Maria Misejova, now Maria Pfeifer, also came under scrutiny. While friends said she loved her son and made sure he ate healthy, others saw another side -- a woman who enjoyed nightlife and the company of wealthy men. One judge said she showed “an appalling lack of credibility.”

But Pfeifer and his ex-wife eventually settled on shared custody. “At that point, we were, you know, co parenting as much as one can,” Pfeifer said.

Meanwhile, Maria Pfeifer moved on and met a new man, Larry Hummel, a Hollywood voiceover agent who proposed to her on his birthday. They married, and they were soon expecting a baby they named Sasha. But just like Maria Pfeifer’s previous marriage, this one ended quickly too.

“I realized, uh-oh this isn't the person that I thought I was with,” Hummel said. “She wanted a very expensive lifestyle, and it was hard to keep up with that.”

Maria Pfeifer left him, and Hummel said it took a toll on him psychologically. He admitted it led to a mental breakdown and he voluntarily checked himself into a hospital.

“I was in a very dark, depressed state because my marriage is falling apart,” Hummel said. “And I think, you know, my belief is, when you’re depressed, you seek help.”

Hummel also reached out to Bob Pfeifer, Maria Pfeifer’s first husband. “It was like, you know, having a mentor in the situation, that he had been through exactly what I was going through,” said Hummel.

“And I said, ‘You don’t understand. You are at war,’” Bob Pfeifer recalled.

Another bruising custody battle ensued, with acrimonious allegations on both sides. But a judge eventually ruled that Larry could have increasingly frequent unsupervised visitations with his son.

"I just wanted what was fair," Hummel said. "She couldn't deal with that."

In the summer of 2012, Maria Pfeifer planned a vacation to her native Slovakia with both Jerry and Sasha, a place she had gone to and returned from often. But not this time.

“That day came and went,” Hummel recalled. “She was not on the plane she said she was going to be on.”

Authorities said what happened to Hummel and Bob Pfeifer is growing increasingly common. The State Department told “20/20” they now see up to 800 cases of international parental child abduction a year.

But the Pfeifer/Hummel case was unique, not only because the alleged abductor had two boys from two different fathers, but because she didn't simply return to her homeland. She disappeared, and authorities were convinced she was a mother on the run.

“It’s tragic enough to take a child away from one of the parents,” Bob Pfeifer said. “It’s another thing to live a fugitive life with a child.”

With Maria Pfeifer failing to return from her vacation with Jerry and Sasha, the Los Angeles courts awarded full custody of the boys to their fathers. Both men got to work searching for their sons, but the weeks soon turned into months.

“The world is too small a place. Everyone leaves a footprint. Also, it’s a mother and two children, how long can they possibly hide for?” Hummel said.

While Hummel hired an international child recovery specialist, Bob Pfeifer spent months meeting with the Los Angeles police and district attorney pressing for criminal charges. On the anniversary of the last time he saw Jerry, Bob Pfeifer was at a turning point.

“We had no money left, had no leads, had nothing to lose, so the idea came up to go public and use social media…to tell the world, to share the message across the Atlantic,” Bob Pfeifer said.

“I helped him build the Facebook page and build “Little Jerry’s Army”…which became huge,” Bob Pfeifer’s friend Stacey Dutton told “20/20.”

In time, the Los Angeles district attorney finally pressed charges against Maria Pfeifer: two felony counts of Child Detention with Right to Custody. If he ever got a solid tip from supporters, Bob Pfeifer knew he had the charges to go after her.

Following a lead from one of Maria’s own friends that she may have been in Paris, France, Bob Pfeifer headed there and, without an appointment, walked straight into the U.S. Embassy asking for a meeting with special agent Eugene Casey with the FBI.

Agent Casey immediately began working on Bob Pfeifer’s leads from his social media campaign. While the Paris lead turned out to be a bust, Bob Pfeifer returned to California and focused his efforts on Slovakia.

“We would take a photo and the message in the native language and literally post it on every Facebook page in the target area, whether it was a bar, a hair dresser, an entertainer,” Bob Pfeifer said. “Thousands of hours went into this.”

Shortly after, reporters in Slovakia learned of the story and helped to further spread the word throughout the country. Through his efforts, Bob Pfeifer then received crucial clues about where Jerry and Sasha were and how his ex-wife might have been disguising her sons that he turned over to agent Casey.

More than a year after Maria Pfeifer went missing with her two sons, agent Casey called Bob Pfeifer and Hummel to tell them their ex-wife was finally about to be arrested by police in Divonne, France, just over the border from Geneva, Switzerland.

Watch the full story HERE to find out if Bob Pfeifer and Larry Hummel were ever reunited with their sons.