Herts Police received a report that a man approached a girl, 10, asking her to go to his car at Oxhey Park at the end of April.
The incident is said to have occurred in broad daylight, at 5:20pm near the cafe located in the park.
A spokesperson for Herts Police said: “Police were called at just before 5.20pm on Saturday 29 April to report a suspicious incident in Oxhey Park, Watford.
“It was reported that a man on a bike had approached a 10-year-old girl and asked her to go to his car, she refused and the man left the area.
“Enquiries are being conducted into the incident and officers are patrolling the area.
Anyone with information which might assist is asked to contact police quoting ISR 668 of 29 April.
“You can report information online at herts.police.uk/report, speak to an operator in our Force Communications Room via our online web chat at herts.police.uk/contact or call the non-emergency number 101.”