More than £46,000 in donations have poured in to father-of-three Christian Smith's JustGiving webpage since he was killed in the crash at 4am on Saturday.
The fundraiser was attempting to circumnavigate the counties of Kent and Sussex in aid of the mental health charity Mind when he was in collision with a car on the A2990, near Chestfield, Kent.
Officers said that they had arrested a 19-year-old man from the Herne Bay area on suspicion of causing death by dangerous driving. He has been bailed pending further investigation until July 27.
It comes after an 18-year-old woman was arrested on suspicion of drink-driving and causing death by dangerous driving and released on police bail.
Pc Jamie Woodhams, of the Kent Police Serious Collision Investigation Unit, said: "Information has come to light regarding a taxi, which is believed to have passed the scene shortly after the collision travelling from the Chestfield/Swalecliffe roundabout towards Whitstable. I do not believe this driver was involved in the collision but I believe he or she could hold valuable information for us."
Mr Smith, from Boughton Aulph in Kent, had set out on Friday to complete his "Kent Epic" of cycling 248 miles around Kent in 24 hours with the goal of raising £1000.
A statement from his family said he leaves behind "a loving wife and three children".
In his last posting on his JustGiving webpage, Mr Smith, who would have celebrated his 39th birthday next week, wrote: "Oh crap what have I done.... 6 days to go. Birthday drinks in Kings Head on 29th March if I am still alive by then."
Describing his fundraising bid, he wrote: "This is an attempt to cycle the full 24hrs, largely unsupported (because nobody is stupid enough to volunteer!). So there are no motorcycle outriders, support vehicles or hot chicks to wipe my brow."