UPDATE 1-Google social network ad business "improving"-Brin

(Adds details, quotes, background)

By Steven Scheer and Rebecca Harrison

JERUSALEM, May 15 (Reuters) - Google Inc (GOOG.O) co-founder Sergey Brin said on Thursday advertising on social networking sites such as Facebook and MySpace was getting better, but was still not perfect.

"In general, it's been improving but we still have a long way to go," Brin told reporters on the sidelines of a conference in Jerusalem to mark Israel's 60th anniversary.

"Things have been going well this year...it's hard to predict where social networking will come out."

Google Chief Executive Eric Schmidt said in January the company was having trouble making inroads selling advertising into what is now the hottest market on the Internet.

Brin said it would take time to find the best formula to develop the social networking advertising business, to develop the right technology and to educate advertisers and users.

"People are expecting overnight to wake up to a miracle... but these things take time," he added.

Brin also repeated that he was "very happy" with a two-week test this month in which rival Yahoo (YHOO.O) used Google search advertisements. But he said he had nothing to add at this stage on any possible further tie-ups.

Microsoft Corp (MSFT.O) withdrew a $47.5 billion offer for Yahoo this month that was aimed at building an online advertising powerhouse to compete with Google. It is now under pressure to find an alternative, such as a search deal with its chief rival.

Schmidt said last week the trial with Yahoo provided good reason for the companies to discuss cooperation, but said there was no deal yet. He said there was a good basis for more talks with Yahoo.

Brin said on Thursday Google was "very happy to have worked with them". When asked about Google's concerns about any partnership with Yahoo, he said that was "hypothetical" and declined to comment.

Yahoo President Susan Decker, who also spoke at the conference, declined to comment on news that billionaire investor Carl Icahn was considering mounting a proxy campaign to replace Yahoo board members after the failed Microsoft bid.

She declined to say whether Yahoo had been in contact with either Icahn or Microsoft. (Additional reporting by Brenda Gazzar; editing by Sue Thomas)