** Mobile advertising firm's shares SITO.O fall as much as
28.3 pct to hit over 1-year low of $2.68 in early trading
** SITO, last down 22 pct, is top pct loser among U.S.
stocks and on pace for its worst day in nearly 1-1/2 years
** Forecasts Q2 revenue well below analysts expectations;
cites near-term challenges of revenue performance and
predictability urn:newsml:reuters.com:*:nGNX8V7042
** More than 757k shares traded, ~4x their 30-DMA
** Including session's losses, stock down 56 pct this year
(Reporting by Amy Caren Daniel in Bengaluru)
((Reuters Messaging:
Amy.CarenDaniel.thomsonreuters.com@reuters.net))