It seems obvious doesn’t it? You always need to thank everyone who helped, everyone who contributed. It doesn’t matter if they are being paid to help or volunteering, ‘thank you’ matters.
There’s no need for a big ceremony. There’s no need for a big speech. A quiet word one-to-one is just as appreciated. If you do go for the ceremony and the speech be careful. Leaving people out when what you’re doing seems highly considered makes people feel slighted – regardless whether it deliberate or not.
Thanking people lets them know they are appreciated.
So, thank you! Even if all you’ve done is read this.