The singer said guitarist Alan Longmuir had been due to join him on stage at Scotfest in Edinburgh on Friday, but he died in Forth Valley Hospital near Stirling on Monday aged 70 after contracting a virus on holiday.
McKeown said: “He would have probably been on stage tonight with me singing Rock And Roll Love Letter.
“I have to stay focused on what I’ve got to do. People are not coming along to a wake, they are coming along to have a party, but we will be dedicating our show to him.
“Also, one song in particular - his first hit song called Keep On Dancing, which he had a hit with in 1971.”
McKeown was speaking as he visited the Glasgow office of children’s helpline Childline, funded by the NSPCC, which will benefit from a collection at Scotfest.
The singer said he has a long association with children’s charities and previously helped raise £35,000 in a night for the NSPCC.
He met Childline volunteers who joined him in singing 1974 hit Shang-A-Lang, and he praised their work in offering counselling sessions for children.
He said: “It’s a very important thing to get the message out that the kids can have the confidence to call places like Childline.
“If they think there’s something not right in their relationship with another person, they should let people know about it, in confidence.”
He said adults could also get in touch regarding historic abuse.
Childline senior supervisor Andy Doherty said the visit and song had given staff at centre a boost, and the money raised would help increase the number of children the service is able to reach.