Do laxatives stimulate weight loss?

Initially. It can help initially - will be harmful in the long run.
No, just poop loss. Laxatives cause only temporary weight loss by making a person poop out stool and water. Poop plus water weighs several pounds a gallon. However, if after excess pooping, a person doesn't eat or drink to replenish himself, his body will be somewhat dehydrated and weak. He will be thirsty, and his electrolytes (such as sodium and potassium) will be out of balance.