A family is seeking help after their daughter was arrested in Japan on suspicion of drug smuggling after crystal methamphetamine was allegedly discovered hidden inside coffee sachets in a parcel she was paid to carry there.

The case builds on recent concerns about the risks faced by "carry-for-hire" couriers who transport packages overseas on behalf of strangers or online customers.

Juthathip Thongnoi, 28, travelled to Japan on July 11 with her boyfriend Sarawut and another friend. The group operated a parcel-carrying service for Thais living in Japan, accepting items from customers in Thailand for delivery abroad.

According to her family, Ms Juthathip was detained by Japanese authorities at Fukuoka Airport on July 12 after crystal meth, known as ya ice, was allegedly found hidden in coffee sachets inside her luggage.

Her parents said they believed their daughter had unknowingly carried the drug and urged Thai authorities to investigate and identify the individual who arranged the shipment.

Mr Sarawut said a customer using the Line name "ing ing" contacted the couple on July 10 and hired them to take a brown box weighing about 12 kilogrammes to Japan.  

Upon arriving in Japan, all members of the group were questioned by airport authorities. Mr Sarawut and their friend were released after several hours of interrogation, while Ms Juthathip remained in custody.

On July 22, the family received a notification through the Thai consulate stating that crystal meth had been found hidden inside coffee sachets.

Of the nine parcels delivered on the trip, all recipients collected their packages except the customer using the name "ing ing", who cut off all contact.

The same customer had transferred 3,600 baht as a delivery fee using an account under the name "HO THI MAI", according to Mr Sarawut.