A member of the public contacted police after spotting the clothing on a fishing platform next to the Aire and Calder canal at Woodlesford, near Leeds, at 6am on Thursday.
Divers from the underwater search unit spent Thursday and yesterday searching the local area as part of police efforts to trace the owner.
The clothes include a pair of light blue jeans in waist size 34, a white Lonsdale polo shirt with a blue motif on the front and an image of a lion on the back, a pair of socks and a pair of white size seven K Swiss trainers.
Detective Inspector John Higson said: "There is no specific information to suggest that the owner of the clothes has come to any harm but it is still crucial that we trace this person as soon as possible so we can establish that they are safe and well.
"I would appeal for anyone with information about who the owner of the clothes may be to contact officers as soon as possible."
He added: "We are concerned about the possibility that the person who left these clothes by the canal may have come to some harm.
"We are now working to find that person and establish whether or not that is the case."