The senseless act hit a marathon walk in Irton which was raising vital funds for Macmillan Cancer Support.
Organisers were left stunned after spending hours creating signs and pinning up the balloons and bunting – only for them to be ripped down and thrown into hedges.
The attack has been branded an “act of cowardice”.
David Parker played a key role in organising the 26-mile challenge, which took place over two days, and saw competitors carry out a number of laps of Irton.
Mr Parker, of Porritt Lane, was devastated by the damage. He said: “Someone was watching our every move.
“After our second lap they crawled out unseen and pulled out the direction signs, throwing them into fields and hedges, even trashing road signs.
“We were all annoyed and very angry and I only hope the people responsible for this despicable act will reflect on their actions and feel ashamed.”
Mr Parker said organisers were upset the day had been tainted, especially after working extremely hard to make it a success.
He added: “We set off around 6.30am to put out the signs on the route to guide people and make sure they were safe.
“We had stalls set up to help support the charity and everything was in place. However, it was on our third circuit that we noticed some of the signs had been removed.
“We initially thought they may have fallen over but on closer inspection, it became obvious they have been ripped up.
“It is so disappointing and a despicable act.
“By my reckoning, this is the first marathon ever to take place in Irton in this way and it is sad that is has been sabotaged.
“A lot of people had put in a great deal of effort and travelled far to take part and help the charity.”
Helen Ferrar told the Evening News she had travelled from Yarm, near Middlesbrough, to take part in the walk.
She said she was equally devastated at the sabotage.
She added: “My daughter and I spent Sunday morning tying balloons and banners to two benches and some flower tubs to raise awareness of the charity.
“We were disgusted when, after the first lap, we found someone had burst all the balloons as well as smashing up the temporary waymarking signs.
“I really cannot understand the small-mindedness of some people.
“I don’t know pleasure did they get out of this at all.
“However, I am glad to say their stupidity didn’t deter us and it actually motivated us all to succeed in our challenge.”