The vehicle, which is used by the Bearded Fishermen charity, was set alight in Sandsfield Lane, Gainsborough, on April 20.
A spokesman from Lincolnshire Police, said: “We are investigating a suspected arson after a vehicle was caught alight in Sandsfield Lane, Gainsborough.
"The fire was reported to us at around 9.50pm on April 20. The vehicle was a Ford Transit Connect.
“Our officers have attended and spoken to the vehicle owner. We continue to engage in and around the Sandsfield Lane area.
“Anyone with any information can call us on 101, quoting incident 465 of April 20.”
Rick Roberts, co-founder of Bearded Fishermen, said: “It is really hard to imagine what goes through the mind of these people, especially as the van is well known around Gansborough and part of Bearded Fishermen Charity.
"It’s mindless acts like this that will one day lead to loss of life.
"Our van was used by Mick on a daily basis to go out around Lincolnshire when he was needed and to help people that were in crisis. Now he can’t get out to the people that need him.
"To target a charity vehicle, no matter what the charity, is such a low thing to do.”
In response people have shown their support for the charity by setting up Go Fund Me pages so the van can be replaced.
If you would like to make a donation to support the charity visit www.gofundme.com/f/isobels-fundraiser-for-the-bearded-fishermen or www.gofundme.com/f/mental-health-emergency-car-fund.
Rory Green, who set up one of the pages, said: “They do amazing work preventing suicides and mental health crisis’ escalating further and they assist the police with their vehicle outreach car which was attacked via arson.
This fire follows another suspected arson in Stanley Street, Gainsborough, on Monday, April 19.
Lincolnshire Police said: “We take all reports of arson very seriously and will carry out investigations into all incidents. If anyone can assist us with either incident they can call us on 101.”