ZURICH, (Reuters) - Activist investor RBR Capital Advisors has launched a campaign to break up Credit Suisse, hoping to capitalise on investor unrest after Switzerland's second-biggest bank lost about a quarter of its value since 2015.

However, the Swiss hedge fund led by Rudolf Bohli, 48, has taken only taken a small stake in Credit Suisse and faces a steep challenge to rally the support needed to succeed.

"With a 0.2 per cent stake, Bohli can't make much progress," Zuercher Kantonalbank analyst Javier Lodeiro and Michael Kunz, who rate Credit Suisse's stock "overweight", wrote in a note.

The campaign comes roughly two years into Credit Suisse chief executive Tidjane Thiam's three-year plan to focus on wealth management and less on investment banking.

RBR, which has been in contact with Credit Suisse's management, wants to divide the company into an investment bank, an asset management group and a wealth manager accommodating the Zurich-based bank's retail and corporate banking operations, an RBR spokesman said.

The strategy, which will be outlined at the JP Morgan Robin Hood Investor Conference in New York on Friday, could see the revival of the old First Boston brand, the name of the US investment bank Credit Suisse took control of in 1988.

Thiam's restructure suffered an early blow when US$1 billion in trading losses prompted him to make even deeper cuts to the investment bank in early 2016.

With the value of the stock diluted by two capital raisings totalling around 10 billion Swiss francs, shareholders are still awaiting the first fruits of the painful overhaul.

Although shares had gained almost 10 per cent this year, the performance reflected only a partial rebound from a feeble 2016 where they fell nearly a third.

"There are enough frustrated shareholders who would do everything to raise the share price," said one Zurich trader.

RBR, partly named after Bohli, was set up in 2003 as a boutique Swiss hedge fund and has around 250 million francs in assets under management.

Based in the small lakeside town of Kuensnacht, near Zurich, it rose to prominence through high-profile but ultimately unsuccessful campaigns against asset manager GAM last year and airline catering company Gategroup in 2016.

Although its stake is relatively small, RBR said it has also signed non-disclosure agreements with around 100 other investors, including some shareholders in Credit Suisse.

RBR has recruited Gael de Boissard, a former Credit Suisse investment bank co-head who left the bank in Thiam's restructure, to support its campaign.

Credit Suisse on Tuesday said it remained focused on its strategy.

"While we welcome the views of all our shareholders, our focus is on the implementation of our strategy and of our three-year plan, which is well on track and which we believe will unlock considerable value for our clients and shareholders," a Credit Suisse spokesman said.

RBR's is the second activist investor campaign involving a big Swiss bank in recent years after Knight Vinke unsuccessfully pushed for UBS to make more drastic cuts to its investment bank.

Credit Suisse has argued keeping an investment bank is vital to cater for the more sophisticated needs of wealth management clients whose assets stretch into the billions of dollars.

But while analysts doubted Bohli's break-up plan would gain the necessary traction with other investors, some agreed that Credit Suisse could still pare back its investment bank even further.

"You have a comparative advantage in the market if you have a private banking and investment banking business," said Mirabaud Securities Limited analyst Andreas Brun, who rates Credit Suisse's stock "buy".

"But you could do it with a smaller investment banking unit than what Credit Suisse has."