BlackBerry co-founder Mike Lazaridis has boosted his stake in the troubled Canadian tech firm with the intention of making an acquisition bid, regulatory documents showed Thursday.

A document filed with the US Securities and Exchange Commission said Lazaridis now has eight percent of BlackBerry shares and is working with another co-founder, Douglas Fregin, "to explore the possibility of submitting a potential joint bid" for the group.

The document said the two "are considering all available options" including "a potential acquisition of all the outstanding shares of the Issuer that they do not currently own, either by themselves or with other interested investors."

The former BlackBerry executives have also hired Goldman Sachs Group Inc. and Centerview Partners LLC to help them study their options, according to the filing.

BlackBerry announced in August after a dismal year that it was looking for a suitor, among other strategic options.

The company that helped create a culture of mobile users glued to smartphones, but lost its luster as many have since moved to iPhones or devices using Google's Android software, later said it had signed a letter of intent for a $4.7 billion buyout by Fairfax Financial Holdings Limited.

Fairfax, a Canadian firm headed by billionaire Prem Watsa, is already BlackBerry's largest shareholder with approximately 10 percent of its shares.

Watsa resigned from BlackBerry's board in August when the search for a suitor began.

But analysts and observers said the proposal was bait to elicit other bids.

Adding to the skepticism, BlackBerry shares have traded below Fairfax's $9 per share offer since the company announced its intentions on September 23.

BlackBerry shares were up 0.37 percent at $8.14 in late New York trade.

Some analysts have said that without a new bid, BlackBerry may need to be broken up to salvage the software and services side of the group, which is healthier than its handset business.

Lazaridis and Fregin started the company, formerly known as Research In Motion, in 1984 using a small government grant, a loan from Lazaridis's parents and monies earned developing a computer display for General Motors.

Early profits from projects such as developing bar code technology for film were ploughed into wireless data transmission technologies that eventually lead to the first BlackBerry in 1999.

Fregin acted as the company's head of operations until he retired in 2007.

Lazaridis quit his role as vice chair in May, nearly 18 months after stepping down as co-chief executive. Forbes magazine recently ranked him as Canada's 17th richest Canadian and 651st in the world.

In January, BlackBerry unveiled a new corporate name and a new platform in January as it sought to regain momentum, but its most recent numbers suggest this has been a spectacular failure.

BlackBerry still has some 70 million subscribers worldwide, but most of these are using older handsets, with the newer devices on the BlackBerry 10 platform failing to gain traction.

Last month, the company announced it was laying off 4,500 staff -- or one third of its global workforce -- after losing $965 million dollars in its last quarter as sales plummeted.