When competitions are done well, they drive the behavior you want and bring people closer together.
When they’re done badly, they incentivise poor behavior, cheating, and drive people apart.
The most common approach is also the worst; have a competition with just one winner.
The problem is the more people who enter, the less likely anyone is to win. Each new person to enter decreases the motivation of everyone else. There’s no reason why anyone would share it, invite others to participate, or even enter themselves.
Luckily there are some better approaches.
The first is to increase the size of the prize with each new participant.
The second is to ensure the top x% of participants win a prize regardless of the number of entries (i.e. top 1%).
Even better, make it a collaborative challenge. Members should have to form teams to enter and solve a series of challenges together. Perhaps consider a tournament format or eliminating one group per week. I guarantee you’ll get more participation and engagement this way.
Once you drop the ‘one winner’ approach, a lot of interesting competition formats begin to emerge.