Alan Willson suffered life-threatening injuries after being attacked by a gang of teenagers in Longcroft Park on Easter Sunday (April 4).
Five teenagers - who cannot be named due to their age - have since been arrested on suspicion of attempted murder and grievous bodily harm with intent, but have been released on bail.
Alan remains in a serious condition in Brighton's Royal Sussex County Hospital.
The attack has devastated the town and a fundraiser to support Alan and his family was quickly set up by Cheryl Edwards and Tara Hobden.
Yesterday the total stood at £3,600, but after receiving national attention donations have now surged past £20,000.
More than 1,100 people have donated and offered words of love and support.
In an update on the JustGiving page, organiser Cheryl Edwards said she and Tara were 'in awe' of people's kindness.
A separate fundraising page, set up by Rhiann Wiseman, has also raised almost £2,000.
You can donate to both fundraisers here:
Help a family after the dads attackedPolice said they are treating the attack as an isolated incident, and officers will be conducting increased regular high-visibility patrols in the area to provide reassurance to the community, and to identify and deter any further criminal behaviour.
The investigation is ongoing and police are urging anyone who saw what happened, or who was in the park around that time and may have any relevant information, to get in touch.
Detective Inspector Simon Dunn, who is leading the investigation, said: “The assault and the build up to it occurred in a public park in daylight, so it was likely that other people would have witnessed the assault or the suspects running from the scene.
“I am keen to hear from anyone who has information but is yet to come forward.”
Members of the public can contact police online or by calling 101 quoting Operation Swallowtail.
Alternatively, information can be passed anonymously to police via the independent charity Crimestoppers online or by calling 0800 555 111.