A missing Long Island teen was last seen at Grand Central Terminal two weeks ago — and police now believe he planned to link up with someone he met on a popular online game, his worried mother said.

Thomas Medlin, 15, was reported missing after leaving the Stony Brook School campus around 3:30 p.m. on Jan. 9 and running to the Stony Brook Long Island Rail Road Station, where he caught a train to the Big Apple, according to the Suffolk County Police Department.

The Saint James boy was captured on surveillance footage arriving at Grand Central about two hours later — and hasn’t returned home or been heard from since.

“He has never left us,” his devastated mother, Eva Yan, sobbed to News 12 Long Island, as she revealed chilling new details into the search for her missing son.

She said investigators believe the teen met someone online through Roblox and arranged to connect with them in New York City — something the heartbroken mom said is completely out of character for her son.

Police recently told the family that the boy’s phone was located in Lower Manhattan and he was recently spotted on surveillance video in Brooklyn, Yan told the outlet.

Medlin’s last known location was near Cherry and Rutgers Streets in the Lower East Side.

“I just can’t believe why he left in the first place,” his tearful father told the outlet, with Yan stressing that they “just want him to be safe.”

Medlin’s distraught parents have teamed up with friends to organize search parties across Long Island and New York City since the youngster vanished.

Police said the approximately 130-pound, 5-foot-4 teen was last seen wearing a black jacket with red stripes, dark sweatpants with white stripes and a black backpack and glasses.

Anyone with information is encouraged to contact Suffolk County’s Fourth Squad at 631-854-8452.