He was speaking at an open meeting in the Guildhall organised by opponents of the proposed sell-off and attended by more than 150 people.
Referring to a possible vote on the sale in November, Cllr Evans said: "We only need a handful of their councillors to switch over to win the day."
He claimed that many Conservative voters did not want to see Citybus privatised, and urged people to contact their local ward councillor and put pressure on them to vote down the sale.
Cllr Evans said: "If your local councillors are Conservative, why not ask them for a meeting so they can explain to you why they want to sell it off?"
The meeting, on Friday evening, allowed members of the public to ask questions of a panel made up of Labour politicians and trade unionists - council leader Vivien Pengelly and the council's chief executive had both declined to send a representative.
The meeting was held just hours after the council announced that it had received five bids from parties interested in buying the publicly owned bus company, and there was an angry roar from the crowd when that was announced.
Addressing the meeting, Plymouth MP Linda Gilroy said the proposed sale was the main factor behind Labour's recent by-election victory in Ham.
She added: "We've got to try and make this Tory administration see sense. What right do they have to do this when it wasn't in their manifesto?
"Would they have won the last two elections if they had put this in their manifesto? I don't think so."
Cllr Brian Vincent, who is a Citybus driver, said commercially operated bus services were not as good value.
He pointed out that Citybus' profits were capped but still generated a regular dividend for the council.
Cllr Vincent said: "There will only be one winner if they sell off Citybus and that will be the fat cats of commercial bus companies."
The council's cabinet is spending nearly £1million on finding out how much Citybus is worth, but says no decision to sell has yet been made.
The process included inviting bids from interested companies, which are currently being considered.
Supporters of privatisation say the proceeds of a sale could be invested more profitably in the city.
Council leader Vivien Pengelly had previously said that she could not attend the meeting due to a personal commitment, but added: "We have not made a decision yet and until we do I can't comment on it. It's too sensitive."
Ian Crews, 54, from Prince Rock, was among those attending the meeting on Friday.
He said: "I think they've already made their minds up to sell it to make money for the Life Centre.
"It should stay in the hands of the public."
ends