Police Scotland have deployed specialist diving teams into the River Leven.
Thomas Brown, 17, was last seen on Friday around 10pm near Methil in Fife by his group of friends.
Insp Andrew Sneddon from Police Scotland said: “It is out of character for Thomas not to be in touch with his family and we are keen to hear from anyone who may have information as to his whereabouts.
“It may be the case that he has met other friends and does not realise we and his family are worried about him. We just want to be assured that he is safe and well.
“Additionally, the area in which he was last seen is well used by dog walkers and I would urge them to let us know if they see anything which may help us trace Thomas.”
If you have information regarding Thomas Brown missing appearance please contact Police Scotland on 101.