The messages have been placed on a fence by the junction of Northam Road and Union Road, along with flowers and pictures.
This comes after a crash involving a silver VW Polo and a white Yamaha YZF motorcycle on Northam Bridge in Southampton at 1.20am on Saturday.
The rider of the motorcycle, from Fareham, died in the crash. Police previously said he died in hospital but have since clarified.
Police say that his next of kin have been informed.
One message, written on a bouquet of flowers, said: “I am going to miss you so much, man.
“I hope you know wherever you are now that I will always be thinking about you.”
Another card, placed on top of a bouquet of flowers, said: “You are my best friend, I always looked forward to seeing you every day.
“I always knew I could rely on you, you were always there if I needed help with my bike, or for a road trip, or to get food. I miss you so much.
“Whenever we were riding you were always right behind me (or miles in front).
“You are so funny and so kind and so clever.
“I can’t imagine my life without you in it. I don’t want to believe you’re actually gone. When we were together, I was the happiest I’ve ever been.
“I love you so much.”
More messages and tributes have been left on the fence from mourners.
Hampshire police are appealing for any witnesses or anyone with footage to come forward, as enquiries
A spokesperson for Hampshire police said: “We would like to speak to any witnesses and, in particular, anyone with relevant dash cam footage of the incident or the moments leading up to it.”
“Anyone with information is asked to call 101 quoting reference 44260192933. or via the Hampshire Constabulary website.”