Lia Seremetis knew exactly how her bike was stolen.

Surveillance video from her Columbia Heights apartment building showed thieves walking into the courtyard with a sledgehammer and breaking the lock that held her single-speed Trek to an iron post.

Losing the bike was a blow in more ways than one. Not only is cycling her main mode of transport, but her bike disappeared just five days before the first anniversary of D.C. Bike Party, a monthly city ride she created that draws hundreds of enthusiasts.

She posted pictures and a description of her bike on message boards and on Facebook, and asked friends to be on the lookout. But after a while, “I had given up,” said Seremetis, 25, who works in public affairs for the Raben Group. “I bought a new bike and kind of let go.”

The experience has become all too common for cyclists in the District and Northern Virginia.

Lia Seremetis rides to work after her bike was stolen and recovered. (Mark Gail/For The Washington Post)

In Arlington County, 380 bike thefts were reported as of mid-October, compared with 233 during the same period a year ago. Fairfax police reported 468 thefts in that period — up 19 percent from 2012. In Alexandria, bike thefts are at a five-year peak. As of late September, 153 had been stolen this year, up 43 percent from last year.

D.C. police reported arresting 98 people for bike thefts in 2012, up from 65 arrests the year before.

The rise in thefts might be partly a result of the District’s success in promoting bicycle use. The percentage of people biking to work in the city increased more than 30 percent from 2011 to 2012, based on data from the U.S. Census, adding tens of thousands more bicyclists to the road.

“There’s more people biking, there’s more bikes on the street and there are more people riding who may not know the best way to lock up their bikes,” said Greg Billing, the advocacy coordinator at the Washington Area Bicyclist Association. “There are definitely professional bike thieves seeking high-end bikes that aren’t locked properly and will sell them for a lot of money.” There are also, he said, “dumb kids looking to do something.”

Metro stations are a frequent target. They have seen a 50 percent increase in bike thefts over the past year, from 202 reports last year to 303 as of the end of August this year, said Morgan Dye, a spokeswoman for the Washington Metropolitan Area Transit Authority.

Rafal Stachowski, 38, a foreign area officer at the Defense Intelligence Agency, moved to Alexandria from Spain last year. He used to leave his bike at the subway “in the worst neighborhood in Madrid” and thought Northern Virginia would be safe. But his bike was stolen from outside the Van Dorn Street station on his fourth commute. Now he bikes all the way to his Springfield office to avoid locking up outside.

Metro Transit Police this summer launched an online registration system to help people recover stolen bikes. And transit police have visited stations, giving away free U-locks to people willing to trade in subpar locks and register their bikes.

“It is important to note that bicycle theft is a crime of opportunity, with the same kind of lucrative payoff as cellphones,” Dye said.

The spike in thefts hasn’t been seen in the Maryland suburbs. In Montgomery County, reports of bike thefts have decreased slightly in the recent past, from 455 in 2011 to 407 in 2012. In Prince George’s County, bike thefts have remained steady over the past few years, said Lt. William Alexander, a spokesman for the county police department.

“I’m not saying people aren’t using bikes in Prince George’s, but it’s not quite the same environment as those northern Virginia communities or in Montgomery County, where there may be a lot more people who ride bikes into work,” Alexander said.

Although lots of bikes disappear, victims have also gotten more aggressive about reclaiming them. Angry bicyclists are posting pictures of their missing bikes on Craigslist, Facebook and sites such as

Jared Janowiak is something of a legend in this community. When three bikes were stolen from the parking lot of his Fairfax condo building in July, he found one on Craigslist, contacted the seller and set up a sting operation.

They arranged to meet at the Arlington Metro; Janowiak brought two friends for backup.

Janowiak ran into some police officers on the way and explained his plan. They were a little “incredulous,” he said, but agreed to help. Janowiak dialed one officer’s number on his phone and put it in his shirt pocket, microphone up — an improvised wire. When he and the thief started discussing price, the police would swoop in.

Janowiak got his bike back and police charged the seller. From there, things get less satisfying. The seller told the police he “bought the bike off a crackhead” in the District, Janowiak said. The other bikes were never recovered. And, Janowiak said, at least 10 bikes were stolen from his building’s garage this summer.

“One conjecture among bike racers,” he said, “is that there’s some hot new bike thieves in the region.”

Many bikes are found. District police post photos of recovered bicycles on their Web site. But authorities said they think many others are moved out of the area.

“We’re not finding the bikes anywhere we would normally find them,” said Lt. Don Hayes of the Alexandria police. A recent meeting with investigators from Arlington and Fairfax revealed that “they’re in same position we are in.”

In one recent case in Arlington, Michael Cullen, 42, was sentenced to eight years in prison for bike theft. Police found pictures of 25 mostly high-end bicycles on his phone; detective Thomas Parsons testified that thefts in the county decreased when Cullen was in custody. But the thief offered little information on where the bikes ended up, saying he sold them to people on the street — a “complete falsity,” according to Parsons.

Seremetis stumbled on her stolen bike by dumb luck.

On a particularly nice September day, she decided to cruise through her neighborhood. Riding up 14th Street, she rolled by a bike parked near W Street NW and thought, “Hey, that looks like my old bike.”

It was the same size and color. Glue was stuck to the front where Seremetis had previously attached a Barbie doll. And there was a dent on the bar, right where her lock had been taken off with the sledgehammer.

Friends quickly arrived with a spare lock to secure the bike. That gave her time to find the serial number and to dig up the e-mail proving she bought it.

Police came and were convinced that the bike was hers. They cut off the lock and Seremetis was reunited with her Trek.