PC Keith Burgess, who was a Southampton neighbourhood officer, sent "flirtatious" messages and acted inappropriately towards the girls in 2014 and 2015.
The 42-year-old was cleared of sending sexually explicit messages, three counts of sexual assault, a child grooming offence and two child pornography charges.
Judge Jonathan Black warned him he faces jail when sentenced on 30 June.
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Married Burgess closed his eyes as the jury returned its verdicts at Guildford Crown Court.
The former officer, who was dismissed from Hampshire Constabulary in 2016, was released on conditional bail ahead of sentencing.
Judge Black ordered the jury to find him not guilty due to insufficient evidence of the explicit messages, sexual assault, child grooming and child pornography charges.
But the jury was left to consider three counts of misconduct in public office, of which he was found guilty of two relating to two girls.
The judge said: "You have been convicted of two matters, you are a man of previous good character and you must realise you face a prison sentence for these matters."
Burgess was cleared of sexually assaulting a 16-year-old in the kitchen of her home while her mother sat in the next room.
But he was found guilty of misconduct in relation to his behaviour towards her.
He was also found guilty of misconduct for sending "flirtatious" messages to a 17-year-old girl and asking for pictures of her in return.
Burgess denied any sexual motive behind sending money to a third girl, aged 15, and said it had been to "help her out" financially.
He was cleared of misconduct and grooming in relation to her.
Deputy Chief Constable Sara Glen, of Hampshire Police, said: "There is no place in policing for those who ignore their professional duty and moral responsibility."
A former police officer has been found guilty of misconduct in public office over "inappropriate" behaviour towards two teenage girls.