King, of Newton Abbot, admitted sexual activity with a child and inciting a child to engage in sexual activity.
He was jailed for 20 months, placed on the sex offenders' register for life and banned from having contact with under-16s when he leaves prison.
The court heard that King, who has since resigned his position as a police community support officer (PCSO) for Devon and Cornwall Police, drove the girl to Teignmouth in March 2006 where he touched her inappropriately.
The court was told that later he approached her in a street when she was with her friends and exceeded his PCSO powers by patting her down after telling her to remove her hoodie top, socks and shoes.
He also sent her texts saying "he found her attractive and loved her and she had a nice body", the court heard.
It was also revealed in court that King had previously been disciplined for stalking female police colleagues and sending them texts of a sexual nature.
The court was told a tribunal had found him guilty of gross misconduct and he was served with a harassment notice and given a written warning but was allowed to return as a PCSO.
Judge Phillip Wassall told the court that King was immature, had developed "some sort of fantasy" and used his police position to exploit his teenage victim.
A spokesperson for Devon and Cornwall Police said: "This kind of conduct by officers and staff is extremely rare.
"Devon and Cornwall Constabulary treat all allegations of this nature, very seriously and swift robust action will always be taken."