Cloudflare, a San Francisco-based firm that provides added security for websites to prevent cyber-attacks, said it would stop protecting 8chan at midnight on Monday, the BBC reported.
The 21-year-old suspect in Saturday's shooting in El Paso, Texas, is understood to have used 8chan to spread his manifesto.
Previously, the site was also used by the suspect in March's shooting in Christchurch, New Zealand, as well as the suspect in April's synagogue shooting in Poway, California.
Losing Cloudflare's protection has made 8chan vulnerable to a Distributed Denial of Service (DDoS) attack, whereby a website is bombarded with traffic that overwhelms its servers, rendering it inaccessible.
A few minutes after the Cloudflare service was withdrawn, 8chan did indeed become unavailable.
However, 8chan's site administrator said that it was moving to another security firm, BitMitigate, based in the US state of Washington.
Cloudflare chief executive Matthew Prince had said, in the wake of Saturday's shootings, that his firm would continue to support 8chan as its policy was to remain neutral over the type of content the service protected, the BBC reported.
However, on Sunday evening Prince wrote in a blog post that "8chan has repeatedly proven itself to be a cesspool of hate".
"They have proven themselves to be lawless and that lawlessness has caused multiple tragic deaths.
"Even if 8chan may not have violated the letter of the law in refusing to moderate their hate-filled community, they have created an environment that revels in violating its spirit."
8chan is a forum created in 2013 by Fredrick Brennan as an alternative to 4chan, a message board popular with gamers.
8chan promised less moderation of controversial topics and images that were being removed from 4chan. As such, 8chan has hosted far-right extremist views and imagery.
Brennan gave up ownership of 8chan in 2015 and has since called for it to be shut down.
( With inputs from IANS )