"Fn dogs," Williams wrote.
"To all Haynsy's family and friends stay strong for him and let God do he's thing I love you all … God always prevails.
"Before I let this be just want to congratulate the victim and the so called justice system you've sent an innocent brotherly to jail away from he's kids you bunch of flops … that's all respectively."
Williams played alongside Hayne at the Parramatta Eels in 2008, finishing his NRL career with 170 matches and 50 tries.
Another of Hayne's former teammates, ex-Warriors and Kiwis centre Krisnan Inu, posted similar remarks to his Instagram on Thursday.
"Not enough words can express how I'm feeling for my lil bro," Inu wrote.
"Don't think justice was served to it's proper intent. To the so called victim. Hope you actually get the help you need, because the things that was said about my boy, wasn't what he's about. Never has, never will be.
"I'm praying for you my Uso. Keep your faith strong like it has been, and let your loved ones come together to help look after your family. Love you Bula.
"And to his loving family, if there's anything youse need, I got youse."
Inu played four seasons at the Parramatta Eels alongside Hayne between 2007-2010, scoring 37 tries in 78 NRL games.
'Appalling' reaction to Hayne sentencing
People on social media labelled the support for Hayne as the "problem with sports mad Australia".
AAP journalist Scott Bailey tweeted: "Some of the comments by former NRL players tonight has been downright appalling. No two ways about it.
"Again, I should clarify it is the minority of former players making the comments. But unfortunately those kind of voices are enough to promote a culture where victims don't feel comfortable reporting sexual assaults."
Sports reporter Mark Gottlieb posted: "Never has the rotten culture inside rugby league been so exposed than by the social media comments of some of Jarryd Hayne's friends and supporters tonight. Most players are good people and they're the ones who should stand up and shout down the ignorant minority.
"If Hayne's friends had come out with messages of support and said they believed he was innocent (despite being found guilty in a court of law) that is perfectly fine but that's not what they did. They targeted their vitriol at the victim. It's despicable. They should be ashamed."
Former Wallaby and acclaimed author Peter FitzSimons tweeted: "Hayne is a rapist and does not deserve public support. Players still playing catch up on how to hold each other accountable."
Law academic at the Australian National University, Dilan Thampapillai, wrote: "It's shocking and disappointing that there are people defending Jarryd Hayne after his conviction. It's worse that there was an attempt to intimidate his victim. We have a long way to go as a society."
Earlier this week, Hayne was spotted with NRL star Corey Norman as the fallen football player tried to enjoy his final days as a free man.
Dragons five-eighth Norman posted a photo to Instagram on Tuesday alongside Hayne and another friend, with the caption: "Catch ups."
Where to get help:
• If it's an emergency and you feel that you or someone else is at risk, call 111.
• If you've ever experienced sexual assault or abuse and need to talk to someone call the confidential crisis helpline Safe to Talk on: 0800 044 334 or text 4334.
• Alternatively contact your local police station
• If you have been abused, remember it's not your fault.
