Police say Maxwell David Yeater, 15, was last seen on a trail at Newman Poses Preserve off Bayberry Lane on Saturday afternoon.
He was wearing navy blue shorts and a navy blue sweatshirt. He is described as a white male with long brown, surfer-style hair.
Westport police said on Sunday they conducted an exhaustive search of the trail on Saturday afternoon but did not find Yeater.
During their investigation, they were contacted by a friend of Yeater's who told police he received a call from him.
The friend gave police the phone number from where the call was placed.
Police say because that number was associated with Wi-Fi calling kiosks located in New York City, they believe Maxwell has made his way to New York City.
The department's bureau is actively working the case. Anyone with information is asked to contact police at 203-341-6000.