Police made house-to-house inquiries in Spalding after a 14-year-old youth was robbed of his mobile phone.
The terrifying ordeal took place around 7.40pm on Sunday in Love Lane, where the youth was walking with his bicycle.
Witnesses reported a knife attack, but police say there was no record of a weapon, but the youth was left shaken.
A spokesman for the police said the attack took place along the low wall in front of St Mary and St Nicolas Church.
The youth heard a man come up behind him and demand: “Stop and give me your wallet.”
It was thrown down when the man saw there was nothing in it, but he took the youth’s Sony Ericsson mobile phone.
A call was received by police at 9.05pm after the youth arrived home.
Anyone with information is asked to call police on 101, quoting incident 905 on Sunday, November 18.