South Wales Police says the search for missing man Ben Thompson is focused on the Canton area of Cardiff, where it is believed he was seen on CCTV at around 7.07pm, near the junction of Leckwith Road and Wellington Street.
House to house enquiries are being done, and residents are being asked to check their gardens and outbuildings.
The 34-year-old from Haverfordwest attended Saturday's Six Nations game at the Millennium Stadium, and was seen by friends in Mill Lane at around 6.30pm.
Chief Inspector Eddie Ough, who is leading the investigation, said: "We are becoming increasingly concerned for Ben's welfare and we are doing all we can to find him safe and well.
"Extensive enquiries are ongoing particularly in the Canton and Leckwith areas where we believe Ben has walked to from the city centre on Saturday evening. I would urge anyone with information of who may have seen Ben to contact the Command Room at Cardiff Bay Police Station on 02920 338 465."
More top news
Missed any of our coverage? You can catch up with Wales at Six here.
The turtle broke records when she was found to have landed in British waters after being carried over 8000 miles.
Barry Rogers is on trial along with his mother for the murder of his 84-year-old grandmother Betty Guy in 2011.