A black teenager who says he has been stopped about 50 times by the Metropolitan police is planning to sue the force, claiming he has suffered almost four years of harassment and false charges, which he believes have been motivated by racism.

Between the ages of 14 and 17, the college student says he has faced a series of charges of which he has either been found not guilty or which have been dropped before getting to court, as well as numerous stops and searches and two strip searches, none of which identified any criminal activity. He says he has also been detained several times in police cells after which he was released without charge.

Last week the teenager appeared at Bromley youth court, south London, charged with assaulting a police officer. The case collapsed after CCTV footage contradicted the evidence in court of PC John Lovegrove, who claimed to have been assaulted by the youth during a stop and search.

The Crown Prosecution Service has admitted it did not review the case fully before it went to court and is to apologise to the youth for allowing the case to go ahead.

The Met police confirmed the acquittal but declined to comment further. However, it is understood concerns about this and other failed charges against the youth, and all the stops and searches, are being investigated by police.

Lovegrove claimed the youth, who was handcuffed behind his back at the time and forced to the ground by police, rolled over and, in doing so, caused grazing and bruising to the officer's knuckles. The youth was also accused of spitting.

However, the CCTV footage in court showed no evidence to support these claims.

The youth's solicitor, James Foong, told the court: "He appears to me to be lying there like a dead fish."

After the court was shown the CCTV footage the CPS offered no further evidence and the case collapsed.

The youth had been stopped by police in Sidcup, south London, on 11 February this year, after reports on the police radio that a named white suspect had threatened his father with a knife and had then run off. The police description was later amended to black or mixed race male.

Although no weapon or drugs were found on the youth, he remained handcuffed while the police forced him to the ground. He was then strip-searched at the police station. He had cigarette papers in his pocket and torn up cardboard that Lovegrove said could be used as a filter when smoking cannabis. No drugs were found during the strip search.

The youth said: "I can't think of any other reason why the police keep doing this to me apart from racism. I've been stopped and searched so many times I've lost count, I think it's about 50 times."

The Met police is 11 times more likely to stop and search black people than white ones, according to Equalities and Human Rights Commission research published earlier this year. It has accused the Met of racial profiling.

"I'm very relieved my son was cleared of a crime he did not commit," said his mother.

"If it wasn't for the CCTV footage, he probably would have been convicted on PC Lovegrove's evidence. But I can't relax because I don't know what the police are going to do next. I'm trying to move the family to a different area that will be safer for us. Because of the way my son is targeted by the police, I'm frightened to let him leave the house. I'm worried he will be arrested again and won't come back."

She added: "I believe my son has been targeted because of police racism. He has been accused of so many things – theft of a laptop, theft of a bike, doing etchings on a wall inside McDonalds. He's also been accused of being part of the Cherry Gang and of harassing young children for drug money. He's never done any of these things."

Lee Jasper, chair of the London Race and Criminal Justice Consortium said: "It is particularly shocking that this has been going on for such a long time and started when the boy was so young. This case exemplifies the harsh realities of being a black kid in London."

A CPS spokesperson said: "This youth was charged by the police with assaulting a constable and our review of the case relied upon a summary of the evidence and other information provided by the police. At trial, it was found the evidence did not support the charge and we decided to offer no evidence against the defendant.

"We fully accept we should have reviewed all of the evidence more thoroughly before the beginning of the trial."

The CPS will apologise to the youth "for not doing so and for not discontinuing the case earlier".

Foong said: "From what he has told me of his treatment and the evidence we have seen in court it would appear the police approach to this young man has been disproportionate and excessive."

The Met police said in a statement: "On 17 August, a 17-year-old male appeared at Bromley youth court accused of assault of a police officer at Sidcup High Street on 11 February 2012 … The case was discontinued by CPS and the youth was formally acquitted."