The lorry was seen stopping on the A168, near the J48 turn off on the A1m, on Thursday evening with around 15 people then exiting the vehicle.
The driver of the lorry, a 49-year-old man from Lithuania, has been arrested on suspicion of an immigration offence. He remains in police custody.
Three other men aged 20, 24 and 29, believed to be from the Kurdish region of the Middle East, have also been arrested on suspicion of illegally entering the UK. They remain in police custody.
Despite tracing a mother and three children, a young woman and a single mother and two children, officers are still searching for five men believed to still be missing.
Police received reports that around five men of Asian appearance were seen walking north on the A1 last night but, despite the use of a police helicopter, they remain outstanding.
The searches for the missing men are continuing today and to assist their enquiries, officers are appealing to members of the public in the Boroughbridge area and towns and villages along the A1 corridor to report any sightings of the men.
A police helicopter was seen circling above the area, helping officers to trace a number of the group including one family, consisting of a mother, father and three children.
They are also appealing to members of the public to check their sheds and outbuildings for signs of occupation in case any of the missing men have taken shelter there.
The group of people already found by police were taken to Harrogate Police Station and have since been transferred into the care of the local authority.
Anyone with any information is asked to contact North Yorkshire Police on 101, select option 1 and pass information to the Force Control Room.
If you have an immediate sighting of the men, please call the police on 999.