Brazil's Green Party presidential candidate is hoping her use of social media will help boost her low poll numbers before October's election as she seeks to close the gap with the two front-runners.

Marina Silva, a rubber tapper turned defender of the Amazon rain forest, had only 10 percent of votes in a recent opinion poll, versus 39 percent for both Jose Serra of the opposition PSDB party and former presidential chief of staff Dilma Rousseff of the ruling Workers' Party.

Analysts said Silva faced an uphill fight making a second-round vote, but that her performance could determine if a runoff is needed. Candidates need more than 50 percent of the votes for an outright victory in Brazil.

Silva said during a visit to New York on Thursday she hoped the use of social media such as Twitter and Facebook could help spread her ideas of environmentally sustainable growth, especially to younger voters.

She said social media was helping make up for the limited TV campaign time allotted her minority party and that she expected people to donate to her campaign through her website.

Every time I look at the polls I get very excited with the results, the 52-year-old Silva told reporters in New York, after two days of meetings with international investors.

We have an average of 10 percent of the votes. If you consider that we just started the campaign, that is very promising.

Silva is the second Brazilian presidential candidate after Rousseff to visit New York, as part of a series of meetings with the international community organized by Brazil's BM&FBovespa exchange, which wants to draw investments to the country.

Silva's vice presidential running mate, Guilherme Leal, owner of the Natura cosmetics company, said Silva was unknown to 48 percent of the electorate despite being a senator from a northwestern Amazon state and a former environment minister under President Luiz Inacio Lula da Silva.

He expressed hope the spread of Silva's ideas through social media networks could spur a turnaround in her polling numbers similar to that seen earlier this year in Colombia and the UK

Colombian Green Party candidate Antanas Mockus surged in opinion polls and forced a second round with former Defense Minister Juan Manuel dos Santos, who eventually won the vote.

British Liberal Democratic leader Nick Clegg rose in the polls after a strong debate performance. His party finished a distant third in seats but formed a coalition government with the Conservatives after no party gained a parliamentary majority.

(Editing by Peter Cooney)