The network said in a statement Tuesday, "We are aware of the media reports and are looking into the matter".
In yet a third tweet, Bellamar accused Piven of assaulting her another time, at the Playboy Mansion.
"And, don't try to deny it, sir", she said in another.
It is unclear if Bellamar is referring to the Entourage series, which ran on HBO from 2004 to 2011, or the Entourage movie, which was released in 2015.
Wisdom of the Crowd, in which Piven portrays a tech genius trying to hunt down his daughter's killer, premiered on 1 October (17).
The allegations made against Piven follow a growing list of actors, directors and Hollywood moguls who have been accused of sexual misconduct in recent weeks.
Bellamar has had small roles in Suicide Squad and The Hangover III, and was featured in the reality shows Beverly Hills Nannies, Millionaire Matchmaker and Jersey Couture.
We reached out to Piven's camp, but haven't heard back.
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