Do I need a work permit for volunteering in Thailand through Helpx or Workaway?

It's illegal if they don't offer you so called volunteer visa etc. Deportation center.. Run.. Pay agent few thousand for bank account and apply visa. You can report that place to immigration..

I was also told by a dog rescue that it would be fine for me to volunteer that it’s “no problem”. But I also researched and learned this is not true. I assume these charities have nothing to lose—they get a volunteer and if you are caught it doesn’t impact them. I hate that I can’t volunteer tho!

Your volunteering is taking away someone's job

How long is the volunteer program?

Sounds like an illegal program. Under the letter of the law you need a work permit to sweep your own floors. A staffed volunteer position would absolutely require a workpermit and id enforced because it taking a job away that could go to a Thai person and be paid if you didn't volunteer.

If it's working exchange of room/board, and no work permit...that a not something that would be consider legal at all and would likely be taken seriously by immigration police.

If you just here on holiday and you take a few hours to some kind of volunteer task every now and then, that's not really an issue. Spending weeks or months with a regular schedule would be a serious issue.

My advice...don't do it. No one wants to see the conditions of immigration jail first hand.

Why would the host care if you're legal or not? You said you're "legally volunteering" but where did you get that idea?

The Thai government considers volunteering to be work. Whether you get paid or not, it is work. To legally work you need a visa that allows work (tourist visa and visa exempt explicitly prohibit work) and you need a work permit. The only way to legally volunteer is with a volunteer visa and a work permit. There is no confusion about this.

Also you ARE getting paid, just because it's not in cash doesn't mean you aren't receiving a payment. That's how those sites work. So it's not even truly volunteer work.

You get a visa for a country BEFORE you travel. You would apply from your Thai embassy for the non-O visa and then travel to Thailand, and then you could open a bank account.

Many people volunteer illegally in Thailand. Just be aware that there could potentially be consequences since you are breaking the law.