Weapons seized included 6in carving knives and pen knives
Kitchen knives have become the most used weapons in teenage stabbings, the Metropolitan Police commissioner said.
About 200 blades have been seized and 210 people have been arrested in the past two weeks in a crackdown on knife crime, Sir Ian Blair revealed.
Speaking at Scotland Yard, Sir Ian said parents "must have conversations about knife crime with teenagers".
Fifteen teenagers have been killed in London so far this year, of which 11 were stabbed.
Sir Ian's announcement came as a nationwide £3m government advertising campaign against knife crime was launched.
The hard-hitting adverts - featuring graphic images such as a man with a knife and a screwdriver in his chest - were designed by teenagers.
Following the deaths of 16-year-old Jimmy Mizen, who was attacked with a shard of glass, and Steven Bigby, 22, who was fatally stabbed in Oxford Street, Sir Ian announced an increase in stop and search operations, codenamed Operation Blunt 2.
During the initiative, several 6in (15cm) carving knives, smaller kitchen blades, craft and pen knives were seized.
Sir Ian said: "We have put search arches in place and in the last two weeks carried out more than 4,000 stop and search operations with more than 200 arrests and nearly 200 weapons seized.
The adverts use the images to illustrate a fictional medical lecture
"To parents, it is tough love time. In addition to conversations about drink, drugs and relationships, there are now conversations about knives.
"The most common knife involved in these deaths is a knife from the kitchen and we must have conversations about knife crime with teenagers," he said.
Cindy Butts, deputy chairman of the Metropolitan Police Authority, said the recent operations targeted 10 boroughs, including Southwark, Lambeth and Croydon.
"The black community supports Operation Blunt. What they do not want is for police officers to go out on fishing expeditions where they cast their nets wide and see what they get back."
Kit Malthouse, London Deputy Mayor, defended stop and searches saying: "Some people out there oppose this type of operation but they come with no other type of solution."
He added that "a little bit of London dies" with every teenager killed in the city.