"r/The_Donald" was among some 2,000 forums or "subreddits" banned as tightening of rules at the news-focused social website, Reddit said.
Twitch, the gaming platform owned by Amazon, said Trump's channel was suspended over rules violations and that the offending content was removed.
"Hateful conduct is not allowed on Twitch," a spokesperson said.
"We do not make exceptions for political or newsworthy content, and will take action on content reported to us that violates our rules."
Twitch said the offending comments aired on the channel included Trump's remarks from 2015 saying that Mexicans coming into the United States were "bringing drugs," "bringing crime" and were "rapists."
Also cited were his statements from a recent Tulsa rally that "a very tough hombre is breaking into the window of a young woman whose husband is away."
Reddit last year "quarantined" the pro-Trump forum for promoting violence, and on Monday removed it.
"Ultimately, it's our responsibility to support our communities by taking stronger action against those who try to weaponize parts of Reddit against other people," Reddit said in a post about its policy update.
The longtime pro-Trump subreddit "has consistently hosted and upvoted more rule-breaking content than average, antagonized us and other communities, and its (moderators) have refused to meet our most basic expectations," Reddit added.
Reddit's new content policy specifically bans promoting hate based on identity or vulnerability, and calls for posts to be personal and authentic to prevent spam.
"All communities on Reddit must abide by our content policy in good faith," Reddit said.
"We banned r/The_Donald because it has not done so, despite every opportunity."
"To be clear, views across the political spectrum are allowed on Reddit – but all communities must work within our policies and do so in good faith, without exception."
The move comes with online platforms facing pressure to crack down on hateful content, including from the president, amid a broad movement to address racial equity in the wake of police killings of African-Americans.
Trump has complained that Silicon Valley platforms are biased against conservatives, despite his own large social media following. – Rappler.com