Twitter downgraded to underperform from perform at Oppenheimer. Stock price target set at $17.Twitter Inc has initiated talks with several technology companies to explore selling itself, a person familiar with the matter said on Friday, signaling the start of what is likely to be a slow-rolling auction of the high-profile but money-losing social media company.A sale of Twitter has been the subject of on-again, off-again rumors for many months as the company grapples with stagnant user growth, soft advertising sales and losses running at hundreds of millions of dollars a year.The company's business struggles have come even as the 10-year-old service has evolved into a potent global source of news, entertainment and social commentary. CNBC, citing anonymous sources, reported on Friday that Twitter is in talks with companies including Google and may receive a formal bid soon. A source told Reuters that Salesforce.com is also in pursuit. What is your price target?