By Gerry Shih SAN FRANCISCO (Reuters) – Twitter shares soared more than 9 percent on Monday to their highest level since the companys initial public offering after a spate of product announcements that could boost its revenue prospects. Twitter has mostly traded in the low-$40 range in recent weeks since November 7, when shares briefly topped $50 in the hours following its highly anticipated IPO. Twitter on Thursday officially began allowing marketers to show individually-tailored ads on Twitter, based on websites the user has previously visited. Apple Inc announced last week it would acquire Topsy, an analytics company that mines Twitter data, for $200 million, according to media reports.