Mr Browder, from North London, said: "I am shocked that the site has had such a large impact.
"When I started Do Not Pay, I thought that it would help a small handful of family and friends.
"I could never have imagined that it would help reclaim millions in parking fines.
"I am disappointed that the councils are targeting the most vulnerable in our society. The elderly and the disabled are disproportionately receiving unfair tickets. The council has a responsibility to protect these groups rather than target them and it is rewarding to do something to work towards that."
The website, which Mr Browder says takes about a minute to generate appeals, asks drivers to choose one of 12 defences for their ticket.
The most popular reasons for appeals are that the parking bay was too small and that the area was not properly signposted.
Others include filling in incorrect details on a permit and information missing from the council's fine notice. Drivers then fill in their personal details and the site generates a letter to send to the council. It is free to use and Mr Browder said he makes no money from the site.
The teenager, who is studying computer science and economics at Stanford University, California, taught himself computer coding when he was 12. He came up with the idea for the website after receiving about 30 parking tickets himself - many of which he successfully appealed - around Camden, North London. All the site's appeals were against council fines, but Mr Browder hopes to cover private car parks too.
Speaking when the website was launched, he said: 'I was given parking tickets for trivial reasons.
'I have come to realise that councils issue tickets first and ask questions later.
'Unfortunately, many recipients of these tickets don't have the time, legal knowledge or energy to appeal.'
Joshua Browder's 12 reasons to appeal
•Warden entered the wrong data on ticket
•Parking bay too small
•Car was stolen before the ticket
•Travelling to hospital urgently at the time
•Bought the car after the offence
•Sold car before offence
•The vehicle has diplomatic immunity
•Paid for the incorrect vehicle
•Missing details on the council's ticket
•Incorrect details on the council's ticket
•Vehicle being leased
•Signage problems
- Daily Mail