Natalie Foster, 18, and her seven-month-old son Robert, live at the Seamer Caravan Site in the Stokesley area.
However, following a violent incident at the location in which a 43-year-old man was seriously assaulted at about 5pm on Friday 22 July 2011, neither Natalie or baby Robert have been seen or heard since.
Two men, aged 30 and 20 from Middlesbrough, have been arrested in connection with the serious assault and remain in police custody.
Enquiries are ongoing to trace one other men, Natalie’s 22-year-old husband Robert Henry Foster, who is from the Southbank area of Middlesbrough.
At this time, the primary concern for North Yorkshire Police is to ensure the safety of Natalie and her child. Extensive enquiries are being carried out and all police forces in the country have been put on alert to assist the search for the mother and child.
Detective Chief Inspector Kerrin Smith, of North Yorkshire Police, said: “As a matter of urgency, it is essential for the police to confirm that Natalie and baby Robert are safe and well.
“There has clearly been a serious and violent incident that has occurred near her home at Seamer Caravan Site in the Stokesley area at around teatime on Friday.
“There is no evidence at this time to suggest that Natalie or baby Robert have come to harm. However, the lack of contact from Natalie with her family in Trimdon, County Durham, since the incident, is very much out of character and a great cause for concern.
“To help put her loved ones’ minds at rest, I urge Natalie to contact the police as soon as possible to confirm that both her and baby Robert are safe.
“I also urge Natalie’s husband, Robert Foster, as well as his family and friends, to fully recognise the seriousness of the situation that has developed and to contact the police immediately.”
Natalie Foster is described as white with a fair complexion, 5ft 2in tall, slim build, dark brown, straight waist-length hair and green eyes.
Baby Robert is white with small features, straight blonde hair with a reddish tint and blue eyes.
Anyone with information that can assist the appeal to trace Natalie Foster and her son Robert is urged to contact North Yorkshire Police as a matter or urgency on 0845 60 60 24 7, quoting the reference number 12110121906.
Information regarding the whereabouts of Natalie and baby Robert, as well as the serious assault, can also be passed anonymously to the independent charity Crimestoppers by calling 0800 555 111.