The incident was reported Sunday around 8:45 p.m. when the victim stopped to use her phone in Duke Island Park.
The victim says the man first held a knife to her throat and demanded money.
She handed over her money and then she told police that the man sexually assaulted her in the nearby bushes.
He got away on a bicycle toward Raritan.
Authorities are asking for the public's assistance with any information. Authorities urge the public not to confront the suspect and notify police.
Anyone with information is asked to to contact the Somerset County Prosecutors Office Sex Crimes Unit at (908) 231-7100 or the Bridgewater Township Police Department at (908) 722-4111 or via the STOPit app.
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