U.S. President Donald Trump accused Twitter Inc on Thursday of restricting the visibility of prominent Republicans on its platform, without providing evidence, and he promised to investigate. "Twitter 'SHADOW BANNING' prominent Republicans. Not good. We will look into this discriminatory and illegal practice at once!" the Republican president wrote in a Twitter post. The practice involves limiting the visibility of a user in search results, specifically in the auto-populated dropdown search box on Twitter. Trump's comments followed a Vice news report on Wednesday that Republican National Committee Chairwoman Ronna McDaniel and other Republicans including Donald Trump Jr's spokesman were being "shadow banned." "The notion that social media companies would suppress certain political points of view should concern every American. Twitter owes the public answers to what's really going on," McDaniel wrote on Twitter. Twitter did not have a comment on Trump's tweet but a spokesperson said the company does not "shadow ban." "We are aware that some accounts are not automatically populating in our search box, and we're shipping a change to address this," the spokesperson said in a statement." Twitter said the technology used is based on user behavior not political views. Twitter instituted a policy change on July 12 to increase the service's credibility and reduce suspected fraud. That change cost its 100 most popular users about 2 percent of their followers, on average, according to social media data firm Keyhole. The change cost former President Barack Obama 2 million followers by the morning after the change and singers Katy Perry and Justin Bieber each lost 3 million, The Washington Post reported, citing analytics company Twitter Counter. The report said Trump's account lost more than 200,000 of its 53 million followers. Twitter shares, already lower in premarket trading after Facebook Inc's disappointing earnings late Wednesday damped enthusiasm for technology and social media stocks, dipped a bit further and volume rose slightly after Trump's tweet at 7:46 a.m. The stock was last down 3.2 percent.