United in Europe, which will be formally registered with the Electoral Commission this week, is spearheaded by Charles Cormack, a former Scottish Conservative candidate who later switched to the LibDems.
Cormack, 44, who runs a business development consultancy focused on the Baltic states, said he and colleagues are concerned by the negative debate around the EU as May's European elections approach.
He said it would be "an embarrassment" if, as polls predict, the UK returned more MEPs from Ukip than any other party.
Prime Minister David Cameron has promised an in-out referendum on EU membership in 2017 if the Tories form the next government, and Cormack said the threat of UK withdrawal is "worryingly realistic and potentially devastating to Scotland and the UK as a whole".
Since using social media to float the idea of a pro-European party to offset the clamour for withdrawal, Cormack said there had been a "pretty remarkable response".
With no detailed policy platform, he said the message would be simple.
"We're standing on a single issue - which is that Britain needs to be at the heart of Europe and needs to be fully engaged and committed to the European Union if it wants to change it," Cormack said. "It can't stand on the outside threatening and throwing toys out of the pram.
"That's not a way to build a relationship - through threats - which seems to be the way the current government are looking to do it."
With interest strongest among 18 to 25-year-olds, the plan now is to field a slate of young candidates in Scotland in May, and possibly also in London.