The National Park Service said six ground crews, including two dog teams, were combing an expanded search area near the Owyhigh Lakes Trail on Rainier's east side. Rescuers also searched by air.
Sykes was reportedly working on a story when she and her partner encountered snow at about 5,000 feet. Her partner stayed as she went on, with the idea that they'd reconvene, but she never turned up.
The partner, who made it safely back to the trailhead, reported her missing at 10:30 p.m. Wednesday.
Sykes had adequate survival gear to camp overnight in an emergency, said Mount Rainier National Park spokeswoman Patti Wold.
Her friends remained anxious but hopeful that searchers will find her safely sheltered.
Safety concerns for Sykes and search crews include snow bridges, tree wells and steep, wet, slippery terrain, Wold said. A searcher was hurt Thursday when he punched through a snow bridge and was airlifted out of the search area.
Sykes is well-known in the Northwest hiking community and has written numerous hiking stories for online publications and newspapers. She is also a photographer and has written a book about hikes in western Washington.
She was working on a story when she disappeared, Wold said.
Her disappearance comes weeks after six climbers are believed to have fallen to their deaths while attempting to climb a challenging route to the summit of the 14,410-foot peak southeast of Seattle.
Close friend Lola Kemp had planned to hike with Sykes this weekend.
"She is the guru of trails," Kemp said Friday in an email, adding that Sykes hiked at least twice a week and has a background in climbing and scrambling. "I find it difficult to imagine that she would get lost. I think it's more likely she's injured and waiting, perhaps impatiently, to be rescued."
Greg Johnston, a former outdoors writer for the Seattle Post-Intelligencer, described Sykes as an avid, strong hiker who knew the mountain extremely well.
"She's the last person anyone would expect to get lost, particularly on Mount Rainier," said Johnston, who recruited Sykes to write a weekly hiking feature for that newspaper, which ran for more than a decade. "If anybody can survive it, it's her. She's really tough and really savvy."
Details on why the search was suspended are unclear. Officials say they will update the public as more information is available.