Richard Dyson, 58, was last seen on November 17, 2019, at around 11pm when he was walking along the A6135 Sheffield Road in Hoyland.
His daughter, with whom he is extremely close to, was due to meet him on November 25, but he failed to show, and she reported him missing.
South Yorkshire Police launched a missing person investigation, but now say they have evidence to suggest he may have been killed, despite no body being found.
Two men, aged 67 and 68, from South Yorkshire, have now been arrested on suspicion of Mr Dyson's murder.
Detective Inspector Neil Coop, in charge of the investigation, said: "Since Richard disappeared 17 months ago, my team and I have worked tirelessly to understand the circumstances surrounding this case.
!Unfortunately, we have not yet been able to trace him and sadly now believe he may have been killed.
“The arrests made today are as a result of evidence that has recently come to light and I hope we will now move closer to having the answers his family so desperately needs.
“As you can imagine, this is an extremely difficult time for Richard’s family, including his daughter. Specially trained officers continue to support her, and I ask that you respect her privacy as she comes to terms with the news she has received.
"This investigation is progressing quickly, and I once again appeal to anyone who has information that may help to come forward. It’s not too late.”
Anyone with information is urged to call police on 101 quoting incident number 459 of November 25, 2019.