Claire Halliday, 35, was last seen in the Fionnphort area in the south west of the island on Tuesday, January 7.
Police said it was “unusual” for her not to be in touch with friends and relatives for this length of time.
Extensive searches have been carried out across the island by police and other bodies, including mountain rescue and coastguard, but she remains missing.
In a statement released on Wednesday, Claire’s family said: “We’re really worried and concerned for Claire.
“We just want to know that she is safe. If you have any information regarding Claire or where she might be, please contact the police to help us safely find her.”
Claire is described as being 5ft 4inches in height, of slight build with shoulder-length, brown, hair.
She has a pink and turquoise eye tattoo on the back of her neck and a butterfly tattoo at the base of her spine.
When last seen she was wearing a white jacket with a cream-coloured hood or hat and white trousers.
Police said she also has access to a Ford Transit campervan, registration WN52 AZP.
They added that she is also known to wear a black beanie hat.
Specialist resources including the Coastguard helicopter and dog branch have been involved in the searches in around the Fionnphort, Loch Poit na h-i and Knockvologan areas.
Door-to-door enquiries have been carried out across the island, and officers have spoken to local businesses and ferry operators.
Officers have also reviewed available CCTV footage from the island.
Inspector Matthew Shaw said: “It has now been eight days since Claire was last seen and we are extremely concerned for her welfare.
“We have received positive responses and support from partners and the community, but I am urging people to think back and get in touch with us, no matter how small it may seem, that piece of information could help us find Claire.”
Anyone with information is asked to call Police Scotland via 101, quoting incident number 1999 of January 9 2025.