The boy was walking on the field in Pontefract Road, Snaith, at around 5.45pm on Monday, when the man started to follow him.
The man didn't say anything to the boy, but tried to grab him twice.
The boy managed to run away to his home.
Police say he was not hurt, but is shaken by the incident.
Detective Inspector Andy Crawforth from Humberside Police said: "We are taking this report incredibly seriously and are following up a number of lines of enquiry to identify the man responsible.
"At this time it is thought to be an isolated report, but I understand that many parents and young people may be worried. I would like to offer reassurance that the local team are patrolling in the area and are there to listen to any concerns you may have.
"He was last seen on High Street heading towards the Co-op. Officers searched the area following the report but unfortunately this search proved negative.
"If you have any information you feel could assist our investigation, or recognise the description of the man, please call our non-emergency number 101 quoting log 480 of March 15.
"We would encourage you to remain vigilant and report anything suspicious to us so we can take the appropriate action."