By BEN FOX
 Associated Press Writer

 TIJUANA, Mexico (AP) — Stepping off a ship in San Diego, David Provost headed south into this border city, where rowdy nightclubs
have lured young Americans for generations. But Provost, a 20-year-old merchant seaman from Florida, never returned.

 Nearly three months later, authorities have found no trace of him in the hospitals, jails or  morgue. Relatives turned up disturbing clues on
their own. His ship, the USNS Bold, set sail without him.

 "If David was just out there roaming around, he would have called, asked for money or something,'' said Pat Provost, his grandmother.
"He wouldn't just disappear.''

 The family in Lutz, Fla., is living in a state of anguish and uncertainty that has become typical for relatives of people who disappear in the
chaotic and crime-plagued cities along the Mexican border.

 No one knows how many Americans disappear in Mexico. In Tijuana alone, the U.S. Consulate gets about 1,200 requests a year to
 find or check on U.S. citizens. Many of these requests are quickly resolved when someone returns from a longer-than-planned
 vacation.

 But ``sometimes they never turn up and we never know what happened,'' said Al Anzaldua, chief of the U.S. Citizen Services section
 at the consulate.

 The citizen services section in Tijuana is busier than that of any other U.S. consulate in the world. On average, five Americans are
 arrested and one dies in its territory each day, leaving little time to chase down those who have vanished in the sprawling
 metropolis.

 Mexican authorities can offer only limited assistance. In Tijuana, state police are overwhelmed with a high murder rate and a large
 number of missing adults.

 Some families with missing relatives also file missing-persons reports with the San Diego police, who can do little more than check
 hospitals and contact liaison officers in Mexico.

 ``It's another country. Our jurisdiction ends at the border,'' said Kathy Bolen, an investigator with the missing-adults unit of the San
 Diego police.

 The reports Bolen receives tend to involve men who were last seen in the strip clubs and discos along the main tourist drag,
 Revolution Avenue, or the even seedier Zona Norte, where prostitution is practiced openly and alcohol is served all night.

 Provost's family fears he has been the victim of a crime. Authorities acknowledge the possibility, given the dangers of the border city,
 which is the base of operations for drug traffickers and immigrant smugglers.

 ``All kinds of things could have happened,'' Anzaldua said. ``You get everything here from homicides to drug overdoses to all kinds
 of crime.''

 In the city of approximately 1.5 million people, there were nearly 300 reported homicides last year, many a result of Tijuana's role in
 the cross-border drug trade. Nearby San Diego, with a roughly equal population, had 51 murders during the same period.

 There have been so many problems over the years that the Marines and the Navy now require junior enlisted personnel to get
 permission before heading south of the border. They are also urged to travel in groups.

 Provost, like the rest of the crew of the USNS Bold, was advised to avoid Mexico, according to police and officials with Maersk Line, the
 company that operates the ocean surveillance vessel under a contract with the Navy.

 A crew member traveled to the edge of Tijuana with him, then turned back when Provost headed off to the main tourist drag, said
 Bolen, who spoke to the ship's captain. ``I think he probably got in over his head,'' she said. ``I don't know where or how.''

 He was last seen on Aug. 21. Over the next two days, there were a series of ATM withdrawals in Tijuana from his bank account,
 totaling about $1,400. Then, nothing.

 ``He would never spend that much money in two days. It's alien to him,'' said his grandmother, a retired bank clerk who helped raise
 him.

 Someone also used Provost's credit card in a hotel in a particularly notorious section of the city known as a haven for smugglers and
 gangs. But it was not the seaman's signature on the receipt.

 And his driver's license arrived by mail at his parents' home in an unmarked envelope, bearing a San Diego postmark.

 The consulate has dealt with kidnappings and fake abductions, in which people try to extort money from their own families. Anzaldua
 knows of cases in which people didn't want their families to know they had been arrested and sent to a Mexican prison. Or, they
 simply want to disappear.

 The Provost family refuses to believe he vanished by choice. Pat Provost's husband and son-in-law traveled to Tijuana to search for
 the missing seaman. The Provosts have spread fliers around Tijuana and San Diego and on the Internet. And they enlisted the help
 of a private investigator.

 "I don't know where to go from here. I don't know what else to do,'' Pat Provost said. ``I'm just so worried. I keep praying.''