He was believed to have earlier spent time in Strathclyde Park with his father before he was reported missing by his family on Sunday, June 5.
Police launched a search for Mr Thomson and appealed to the public for help to find him.
Officers confirmed on Friday that a body had been found in the search for the 18-year-old.
The body has not yet been formally identified but police believe it to be that of Mr Thomson. They are not treating the death as suspicious.
A Police Scotland spokeswoman said: “At around 3.15am on Thursday, police were called to a report of the body of a man having been discovered in a wooded area close to Kilbrennan Drive, Motherwell.
“The body has not been formally identified, however, it is believed to be that of missing man Robert Thomson from Bellshill. Relatives are aware.
“A post-mortem will take place in due course to establish the exact cause of death, which is not being treated as suspicious at this time. A report will be sent to the procurator fiscal.”