Thousands of people have taken to social networking sites to raise awareness of Tia’s disappearance.
The Facebook Group Help Find Tia has nearly 10,000 members, with hundreds of concerned people across the country asking to be emailed posters so they can be displayed in different cities.
A number of celebrities including Coleen Nolan and pop star Jessie J, have helped publicise the search on Twitter.
In a bid to trace Tia, police released a new CCTV image of her which was taken outside the Co-op on Featherbed Lane, New Addington, the day before she went missing.
The CCTV still shows Tia wearing similar clothes to those she was last seen in. Tia, who has never been missing before is white, of slim build, 4ft 5ins tall and was wearing French Connection UK
glasses with her hair tied back.
She was last seen wearing a yellow bandeau top over a white bra with visible cross straps, light grey leopard-skinned leggings and black and pink Nike high top trainers.
Detective Chief Inspector Scola said: "Searches are continuing at Tia's grandmother's address, CCTV is being collated and viewing continues.
"We have recovered a number of items but we now know that they do not belong to Tia."
Anyone with information should call the incident room on 0208 721 4005 or Missing People on 116 000 quoting reference 12MIS025216