UPDATE: The Portland Police Bureau announced Thursday morning it was canceling the news conference due to "unforeseen circumstances."

Even in a city that has spent millions on bike-related infrastructure and earned the nickname Bike City U.S.A., it's hard to catch a bike thief. It's even harder to prosecute one.

Portland thieves last year took more than 2,100 bikes worth well over $1 million combined, according to an analysis by The Oregonian/OregonLive using Portland Police Bureau data. That number, reflecting only those thefts reported to police, is nearly two times what it was in 2007.

The bike theft database, containing 13,000 records, shows an arrest in about 2 percent of such cases.

The bureau provides an online form for crime victims to report bikes stolen, but those reports "are not reviewed on a regular basis by anyone," spokesman Sgt. Pete Simpson wrote in a recent email.

The issue matters to a broad segment of Portlanders. About 29 percent of adults in Multnomah, Clackamas and Washington counties own a bike, according to a 2011 Oregon Household Activity survey. Census data show about 6 percent of workers in the city commute by bicycle.

A Thursday news conference, scheduled by Portland police to announce the formation of a new bike theft task force, comes after years of concerns raised by Portland bike enthusiasts that justice is not being served.

Some theft victims have been so frustrated when police were unable to help recover their property they've taken matters into their own hands.

One activist talked about planning a meetup with a suspected thief near a police precinct office hoping to put pressure on police to come and help. It's a strategy activists experimented with in Oakland and is now moving up the coast.

"Is it worth getting stabbed with a rusty screwdriver by a tweaker for a bike? Many people say no," said Bryan Hance, founder of the website StolenBikeRegistry.com. "But some say: 'That was my Dad's bike, it has sentimental value, and I want it back.'"

Hance said the police bureau's plan to create a task force that includes police and advocates is a model that's worked in other cities.

"It's been a long time coming," he said. "Portland really needs this."

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It might not take many convictions to put a big dent in Portland's bike theft problem. Prosecutors say it's likely most of the bikes stolen in any given year pass through the same two dozen hands.

"The 80-20 rule applies -- 20 percent of the criminals doing 80 percent of the damage," said Kevin Demer, Multnomah County deputy district attorney in the felony property crimes unit.

An array of mugshots of suspected bike thieves hangs next to the cash register in the Bike Gallery store downtown.

Portland has a cast of so-called "frequent fliers," authorities say. Downtown bike shops have posted an array of mug shots showing people they consider chronic suspects in bike theft.

Police may have stopped these individuals, many of them homeless, on more than one high-end, carbon-fiber bike with clipless pedals and disc brakes. But their court records often don't reflect a pattern of theft convictions.

Prosecutors routinely dismiss the theft charges that police lodge against them. Most frequently, prosecutors say, that's because there's not enough evidence.

"These are not slam dunk cases," Demer said. "Let's say we know it's your bike because we have your serial number. How do we prove that they know it was stolen?"

Unless the thief admits the crime or is trapped in a lie that shows he or she knew the bike was stolen, the case is sent back to the police bureau. The case would fall to property crime detectives whose priorities are largely dictated by dollar values. Burglaries and car thefts take precedence.

Bike theft cases fall to the bottom of the heap, and few are investigated unless the current value of the bike is more than $1,000, the threshold at which the crime becomes a felony, prosecutors say.

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Information gaps pervade the system, starting with the fact that many thefts aren't reported.

Vicki Quick, for example, didn't bother to report it when her daughter's bike was swiped off the porch of her Southwest Portland home last year.

The bike didn't cost much, and it was unlikely to be recovered, Quick reasoned. She also thought the theft would serve as a lesson in consequences for her teenage daughter.

"I had warned her to take better care of her bike," Quick said. "That's what happens. It's cause and effect."

Like Quick, many cyclists say they see little point to filing a police report, unless they need one for an insurance claim.

Portland police estimate they receive reports on only 70 to 85 percent of bike thefts. That may be optimistic. The federal Bureau of Justice Statistics found in 2013 that apart from burglaries and car thefts, victims report less than one-third of property crimes to police.

A comparison of Portland police data with counts maintained by local universities, which are particular hot spots for bike theft, show that students may report as few as 1 in 10 cases to police.

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When thefts do get reported to the police, it's unclear what happens next.

Simpson, the police spokesman, declined to make a detective available to describe how bike theft cases work their way through the system. He said if a report indicates a serial number, records staff type the information into a database.

Bike advocates say online reports can linger in a kind of electronic purgatory for as long as two weeks.

"There's this huge window in which that information is not available to anybody," said Hance, the Portland bike activist. "That's actually the window in which a bike is most likely to pop up."

To address what he perceives as that information gap in police reports, Hance started StolenBikeRegistry in Tucson and now runs BikeIndex.org with Chicago-based Seth Herr. BikeIndex.org allows users to enter information about stolen bikes and makes it visible to the public.

Hance said unofficial registry sites like BikeIndex.org, in conjunction with Twitter and Facebook, have succeeded in recovering thousands of stolen bikes. The stream of tweets, posts and comments when a theft is reported is nearly torrential.

Portland resident Jeff Michael used the service six months ago and was pleased when a BikePortland.org reader emailed him to say he thought he saw Michael's high-priced LeMond bicycle listed on Craigslist.

Michael was able to arrange a meeting with the seller and told police in advance. They said they would come but didn't show up, Michael said.

The seller showed a frame that bore the same stickers, dents and scratches as Michael's bike. But the serial number on the bottom of the frame had been filed off and the custom parts stripped and replaced with cheaper ones.

"I was just so sick to see the frame that I just let him keep it," Michael said of the teenage seller. "I just couldn't bear it."

Jeff Michael's bike was stolen Feb. 2 in front of the 24 Hour Fitness in the Pearl District.

Michael bought a less expensive bike as a replacement. But someone stole that one Feb. 2 from the bike cage in front of the Pearl District 24 Hour Fitness.

He said he filed a police report just to add legitimacy to his post on BikeIndex.org, a community he approvingly labels "vigilantes." He said he no longer has faith in Portland police.

"They're not going to find the guy," Michael said. "They're not even going to look."

The police bureau's Simpson, without commenting on the specifics of Michael's assertions, said generally that police "have to prioritize investigations based on the availability of tangible leads in the case balanced against the other demands of investigators and community complaints."

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Advocates hope Portland police may be starting to see the potential to capitalize on a community already organized and motivated to help.

Bike activists report a better working relationship with law enforcement since a bike theft summit that Jonathan Maus of BikePortland.org organized in December with police and prosecutors.

Online crowdsources like BikeIndex.org may become part of the solution for police.

BikeIndex.org provided a stripped-down version of its database for police to easily access in patrol cars, and the group recently launched a system to collect serial numbers at some local bike shops the moment of sale.

The Bike Index team also created a Twitter identity @IsItStolen. Users tweet a serial number to @IsItStolen, which then automatically tweets whether or not the bike is in BikeIndex.org's database.

Project 529, an anti-bike theft group that's a relative newcomer to Portland, uses the geolocation function on smartphones to send out an alert to all its users within a 10-mile radius when a bike's status is switched to stolen.

"It's like Neighborhood Watch that can help catch a thief before they pedal out of the zip code," said J Allard, the company's CEO.

The Project 529 app can directly notify law enforcement and create posters about a user's stolen bike with the click of a button. Recently, the company teamed up with BikeIndex.org to allow simultaneous searching of both databases.

Crowdsourcing sites have a much broader reach than the police do, said Hance, of BikeIndex.org.

"Our system," he said, "is where the eyeballs are."

Mark Friesen of The Oregonian staff contributed to this report.

-- Carli Brosseau

cbrosseau@oregonian.com

503-294-5121; @carlibrosseau