Boris Johnson was greeted by more than 100 campaigners hoping to save the axed N213 night bus when he came to Croydon on Wednesday night.
The protest was organised by Sutton student Laura Wheeler, 22, using facebook, the social networking site.
Nearly 4,000 people have joined the group online to save the N213, the only night bus route between Croydon and Sutton.
The route was cancelled on July 4.
Campaigners fear vulnerable young people will be forced to take unlicensed cabs or walk home after a night out in Croydon.
They are also concerned Sutton residents working in Croydon’s clubs and bars will have no way of getting home late at night.
Miss Wheeler personally handed a 4,000 strong petition to the Mayor outside Fairfield Halls.
She said: "There were about a hundred of us standing outside Fairfield Halls when Boris arrived and he did a news interview with us in the background, so our campaign has gone national.
“I personally got to have a one on one with Boris. I said we have over 4,000 members on our facebook group and he did not say anything. He looked shocked.
“I also went into the Mayor’s debate and Councillor Steve O’Connell allowed me to have a question.
“I asked him what he was going to do.
“He said he was a bus lover and this was now the most famous bus in London, which made us smile.
“He did take it seriously though.”
The campaign has attracted the support of Sutton MP Tom Brake and Coun Steve O’Connell, the Sutton and Croydon Greater London Assembly representative.
In answer to Miss Wheeler’s question Mr Johnson said: “I understand what you say and thanks for the demonstration earlier on.
“I have got the petition. I know the strength of feeling and I am going to take it back to TfL and I am going to ask them next time they decide to cancel a night bus can they make sure I am not going to speak in the borough where the cancellation is taking place.
“The point you have made is a good one. It is about the security and safety of people and night buses play an important part especially for female passengers. And there are economic benefits.”
Miss Wheeler, who is meeting with Transport for London (TfL) next week said she was confident the Mayor would do all he could to help them reinstate the bus.