BEIJING — Liu Lijing, a mechanic in Beijing, does not usually pay much attention to manners. He does not mind when people blast loud music, and he strolls the alleyways near his home in a tank top stained with grease. But when a stranger recently ditched a bicycle in the bushes outside his door, Mr. Liu was irate.

Start-ups have flooded the city with shared bikes, he complained, and people have been leaving them all over the place without thinking about other residents. “There’s no sense of decency anymore,” he muttered, picking up the discarded bike and heaving it into the air in anger. “We treat each other like enemies.”

There are now more than 16 million shared bicycles on the road in China’s traffic-clogged cities, thanks to a fierce battle for market share among 70-plus companies backed by a total of more than $1 billion in financing. These start-ups have reshaped the urban landscape, putting bikes equipped with GPS and digital locks on almost every street corner in a way that Silicon Valley can only dream of.

But their popularity has been accompanied by a wave of misbehavior. Because the start-ups do not use fixed docking stations, riders abandon bicycles haphazardly along streets and public squares, snarling traffic and cluttering sidewalks. Thieves have taken them by the tens of thousands, for personal use or selling them for parts. Angry and mischievous vandals hang them in trees, bury them in construction sites and throw them into lakes and rivers.