UPDATE 1-Global ad business improved in April - WPP

* WPP says April was first month of worldwide growth

* Sees grounds for optimism in 2010

(Adds quote, details, background)

MOSCOW, May 12 (Reuters) - The global advertising business is showing signs of recovery after months of decline, WPP Plc (WPP.L), the world's top ad firm by sales, said on Wednesday adding its own business saw worldwide growth in April.

"We've just seen what we call our flash numbers for April, which did show that change from what we saw in March, so we are starting to see for the first time growth in our business on a worldwide basis," said Martin Sorrell, chief executive.

WPP last month raised its like-for-like full-year revenue forecast to 2 percent growth from a previous prediction of a flat result after a strong turnaround in the United States, and Sorrell now says even that forecast might be a little pessimistic.

"We did see a significant change in April," Sorrell told Reuters Insider Television on the sidelines of a two-day conference of the International Advertising Association.

Some of the world's top advertising and marketing heads are meeting at the conference in Moscow to consider growth strategies for the $450 billion industry. [ID:nLDE649132]

Global advertising spending is expected to rise 2.2 percent this year, driven by online paid-search ads, according to media buyer ZenithOptimedia, which is part of the Publicis (PUBP.PA) agency group.

In Russia, according to the Russian Association of Communication Agencies (RACA), ad placement rose by 5 percent on the year in the first quarter to 46 billion roubles ($1.5 billion). (Reporting by Maria Kiselyova and Kiryl Sukhotski; Writing by Lidia Kelly; Editing by David Holmes) ($1=30.29 Rouble)