Their parents and loved ones have set up Web sites, distributed fliers and searched through back alleys and alongside rivers. They have pumped friends for slivers of information and asked anyone who knows anything to please, please, come forward.

But still there is no trace of four young adults -- three male, one female -- who disappeared from Minnesota and Wisconsin over a 10-day stretch beginning last month.

Each had been drinking, and the schools three attended are near Interstate 94. Otherwise, there is no concrete evidence to suggest that the cases are related, or even that something untoward has happened.

Still, their families have sought one another out for support and leaned on experts such as Patty Wetterling, a national advocate for missing children whose son, Jacob, was abducted 13 years ago in St. Joseph and never found. Wetterling knows too well what the families are going through: pushing law enforcement to do more; trying to get as much media attention as possible; talking to friends, neighbors and associates in the hope that their insistence will jar a memory that will lead to their loved one -- even if to a corpse. Not knowing, she said, is the hardest part.

"The problem and frustration is that people simply can't vanish," said Wetterling, surrounded by photos of her missing son and other missing children and adults in the offices of the Jacob Wetterling Foundation here. "It's a serious problem."

An average of 17,000 Minnesotans are reported missing each year, authorities said. Few are victims of homicide or any other crime; some simply choose to disappear for a while and eventually return home. Most are 17 or younger. Nationally, as of Nov. 1, there were 42,310 active cases involving missing adults and 55,316 cases of missing children 17 and younger, according to FBI statistics.

Throughout Minnesota, the issue has received plenty of attention as a result of the four recent cases.

Erika Dalquist, 21, disappeared in Brainerd on Oct. 30 after leaving the Tropical Nites bar with a man she recognized, according to friends who had been with her earlier. No money has been taken out of her bank accounts since then. Just this week, police said they were investigating her disappearance as a criminal matter. Her mother, Colleen Dalquist, made this televised plea on Monday: "Please have a conscience. Let us have our daughter home for the holidays."

On Halloween night in downtown Minneapolis, University of Minnesota student Christopher Jenkins, 21, disappeared after a night of heavy drinking. He was dressed in a Native American costume and had neither his cell phone nor his wallet with him. His parents drove from suburban Milwaukee to set up a headquarters in Minneapolis, organized hundreds of volunteers to search for their son, and hired a private investigator. Police don't suspect foul play, but his parents remain unconvinced.

Michael Noll, 22, disappeared in Eau Claire, Wis., on Nov. 6 after leaving the Nasty Habit Saloon alone after a birthday celebration. The University of Wisconsin-Eau Claire student apparently stumbled into a neighbor's house, and his hat was found nearby. Search dogs led police to the Chippewa River near his house but found nothing.

Joshua Guimond, 20, went missing from St. John's University in Collegeville, about 75 miles northwest of Minneapolis, on Nov. 9. Around midnight, he took a break from writing a paper and left to play cards. He didn't take a jacket or his contact lens case. His car was found on campus.

Some families have a hunch the cases are related. "We think there's a very good chance it's connected," said Paul Cheney, Guimond's uncle. His nephew "was a highly motivated, very intelligent, very focused individual. He had every intention of going to law school."

Police were notified of his disappearance about 24 hours afterward. They immediately assigned someone to the case and began interviewing family members, talking to friends and searching the area where he was last seen. That's common practice in Stearns County, said Sheriff Jim Kostreba, whose department remembers the case of Jacob Wetterling vividly.

"It's best to be involved immediately," he said. "Obviously, we don't have the number of runaways and missed people as a major metropolitan area. But no matter what you do, the family is always frustrated because they always think you should be doing more."

Cheney said he thought that the investigation into his nephew's disappearance was "going a little slow" and that getting information was like "pulling teeth."

Meanwhile, Steve Jenkins, Christopher's father, said all he'd gotten from Minneapolis police was the runaround. They made the family wait for 72 hours before accepting a report on the case, he said, and now have told family members that they think their son may have fallen into the Mississippi River -- and that his body would surface when the water warms up in the spring.

Jenkins isn't buying it.

"Any parent that has to deal with a missing child should be a challenge enough," said Jenkins, who stayed in Minnesota for two weeks straight looking for his son. "What Minneapolis police have done is also forced us to beg to keep this investigation alive, and I mean literally beg."

Minneapolis police, however, said they had followed up on every lead, assigned a sergeant in homicide to the case full time and had its water patrol searching. "It's still an open case," said police spokeswoman Cyndi Barrington. "Unfortunately, we haven't found him yet."

Wetterling said the push and pull between relatives and authorities is understandable. Parents believe that their child's case ought to take precedence over whatever else the police are doing, and are often shocked to learn that their case is not as high a priority as they would like.

That's why Wetterling is pressing state leaders to set up a statewide task force to come up with uniform guidelines and trained leaders who could mobilize quickly in such cases and determine whether a particular case of a missing adult has the same urgency as child cases.

"The timeline in adult cases varies by department," she said. Some require a 72-hour wait before they will look for adults. Others go into action immediately, regardless of age. The basic premise, Wetterling said, ought to be that police can do something for every family, including filing their names in the nationwide database of missing people, issuing a statewide police lookout and visiting the last place the person was seen.

Parents, she said, aren't unaware of the grim statistics. Seventy-five percent of children who are snatched, for instance, are killed within three hours. And the longer a person is missing, the less likely he or she is to be found alive.

Still, they hope. Wetterling wears a button with a computer-enhanced picture of her son as he would look today if he is still alive.

"Parents will always hope that there is a chance," she said, prodding others to keep the same vigilance. "We cannot just accept that [our children] just sort of disappear. That's just not acceptable."

Patty Wetterling, right, hugs Connie Larson, with daughter Jayme at her side. The Larsons were honored as crime victim advocates, and Wetterling received an award for her continuing crusade in the fight for child safetyErika Dalquist, 21, missing Oct. 30. Chris. Jenkins, 21, missing Oct. 31. Michael Noll, 22, last seen Nov. 6. Joshua Guimond, 20, missing Nov. 9.