An avid hiker has been missing since Friday and search efforts, including those of a 70-strong volunteer group, have not turned up any clues.

Mr Steward Lee, 27, left his home in Bukit Panjang presumably for a hike on Friday afternoon. He was alone, in slippers and did not take his phone with him.

His family made a police report on Friday night. The next day, the police put an appeal on their Facebook page.

On the same day, his sister, Ms Lee Yunqin, 29, a researcher, posted a request on her Facebook page for volunteers to conduct a sweep of nature areas.

"We think that he may be in one of the parks... but the police need help covering the ground, especially in off-trail areas," she wrote.

Speaking to The Straits Times, she said her brother went hiking almost every day and this is the first time he has gone missing.

"We saw him on Thursday, but we didn't know what time he left on Friday," she said.

Yesterday, the search party, made up of police officers, park rangers, family and friends scoured Singapore's parks and nature areas from 9am.

About 60 of the volunteers combed popular hiking areas, including the Bukit Timah Nature Reserve, Dairy Farm and Singapore quarry area, Mandai, Zhenghua Park and the rail corridor.

By about 12pm, they still could not trace his whereabouts. He was still listed as missing as of 11pm yesterday.

Mr Lee, who is unemployed, would always inform his family if he was staying out, Ms Lee said.

The 1.79m-tall man was last seen at Block 407, Fajar Road at around 2pm on Friday. He was wearing a black T-shirt and jeans.

A group of friends and family members have been searching for him since Friday night. They covered areas in Bukit Panjang and libraries, which he frequents, Ms Lee said.

"We're really worried, anyone who has any information can come forward."

They may call the police on 1-800-255-000.