McCartney regularly took the violin-shaped Höfner 500/1 electric bass on stage from 1961 to 1963 until it disappeared just before the band broke up at the end of Beatlemania.
He previously said he “fell in love with it” because its shape looked more symmetrical as he played left-handed.
Ever since, the Help! superstar has been on the hunt for the Höfner.
Though he briefly put it to one side during his time in the band, he picked it up again for recording sessions in London when the group were recording hit Let it Be.
The guitar can also be spotted in Get Back, Peter Jackson’s documentary released in 2021.
Now, Höfner have stepped in to help the musician with his desperate search for the instrument, which is now valued at around at least £10m due to its extensive musical history.
The search has been launched online with the hashtag #tracingthebass inviting people from around the world to help track it down.
Höfner executive Nick Wass told the Sunday Telegraph: “I’ve worked closely with Paul McCartney’s team over the years, and when I’ve met Paul we’ve talked about his first Höfner bass and where it could be today.
“Paul said to me, ‘Heh, because you’re from Höfner, couldn’t you help find my bass?’ And that’s what sparked this great hunt.”
Welcome to The Lost Bass Project - the global search for Paul McCartney's original Höfner bass. Between 1961 and 1969 this bass changed the world. Today it's the Holy Grail of Rock and Roll. Follow the trail. And help trace the bass. Visit https://t.co/4eZFkyULMv @tracingthebass pic.twitter.com/VauQW8G9bB
— TracingTheBass (@TracingTheBass) September 2, 2023
Rumours vary from a thief taking the bass from a closet at Abbey Road to a story that it vanished from the basement of the Beatles’ Savile Row offices.
Mr Wass added that the bass could be valued “more like a Van Gogh or a Picasso than just an instrument”, adding: “This is the bass Paul played in Hamburg, at the Cavern Club, and at Abbey Road.
“Paul would be so happy, thrilled, if this bass could get back to him.”
Since launching the project yesterday, organiser Scott Jones said on Sunday: “We are dealing with hundreds of emails and we’ve already picked out two (emails) in particular, because we know it instantly marries up with something that was known before.
“We didn’t expect to get necessarily thousands of super-hot leads instantly … what I’m anticipating is that people who know something will probably just sort of reflect on what they know and then come forward at some point.”
When asked about the details of the leads, the 56-year-old said he could not give an individual’s name, who has been mentioned by “different people”, but they had connections to the UK and America.
Mr Jones, a journalist who investigated the death of The Rolling Stones guitarist Brian Jones, added: “The name (has) cropped up a few times now, because it’s disconnected and it’s coming from a range of sources. Obviously, things like that stand out.
“It’s all still possible but it’s a much stronger feeling you’ve got about a piece of evidence like that if it’s being effectively supported by totally independent and unconnected people.”