FRANKFURT (Reuters) - Commerzbank (>> Commerzbank AG) aims to add 2 million retail and small business customers over the next four years, part of a revamp to boost earnings that will also see it cut thousands of jobs.

Germany's second biggest lender detailed its new strategy on Friday as the chief executive of Deutsche Bank (>> Deutsche Bank AG) sought to reassure staff and investors that the country's largest bank remained robust after fears over its stability sent tremors through financial markets.

Commerzbank's new customer drive will be based on greater use of multi-channel banking and products such as a digital loan platform and robot-assisted asset management advice.

"We've started to see movement in market share that appeared fixed in cement over decades and that is our opportunity," Chief Executive Martin Zielke told a news conference, adding that Commerzbank's 1000-branch strong network would capture clients abandoned as rival banks reduce their geographical presence.

Deutsche Bank and HVB (>> UniCredit SpA) have been closing branches in their own efforts to boost earnings.

Commerzbank's target is double the previous goal for net new retail customers over the last four years, which it achieved.

It also aims to boost its market share among small businesses to 8 percent from 5 percent, helping to generate revenue growth for the retail and small business segment of at least 1.1 billion euros (£946.85 million) by the end of 2020.

Negative European Central Bank (ECB) interest rates are limiting the scope to boost revenue in a fiercely competitive German banking market, leaving Commerzbank little choice but to focus heavily on cost cuts.

Zielke, who has been working on the plan since taking the helm in May, said he intends to generate 1.1 billion euros in savings through improved efficiency.

His plan aims to cut the ratio of costs-to-income, a key measure of profitability, to below 66 percent, while boosting return on tangible equity to more than 6 percent over the period.

The cost-income ratio currently stands at 83 percent and return on tangible equity at 3 percent, credit rating agency Fitch calculated, underscoring Zielke's ambitious path ahead.

"We see substantial execution risk, primarily in defending its corporate market position," Fitch said in a note, adding that cutting jobs were likely to involve lengthy negotiations.

Commerzbank had outlined its plan on Thursday, including the nearly 10,000 job cuts, more than a fifth of its workforce. Zielke said he would try to avoid compulsory redundancies.

The labour representatives on Commerzbank's supervisory board said in a statement they supported building up the bank's core business and the need for digital operations but added that the size of the job cuts was not justified.

Mark Roach, one of those members, told Der Spiegel magazine the actual number of employees affected by the job cuts could be more than 12,000, because of the bank's many part time workers.

Shares in Commerzbank were 3.5 percent lower at 1430 GMT, lagging a 0.7 percent drop in the STOXX Europe 600 banking index <.SX7P>.

(Additional reporting by Jonathan Gould; Editing by Alexander Smith)

By Alexander Hübner

Stocks treated in this article : Deutsche Bank AG, UniCredit SpA, Commerzbank AG