It's easy to come up with similes about being lost. Being lost is like being trapped in a maze and not knowing which way to turn. Being lost is like being a single cloud alone in the sky. Being lost is like being at a party where everyone is a stranger. These are not good similes, but they are similes.
I think coming up with a good simile depends on understanding what the feeling of being "lost" means to you. Maybe you can remember a time when you felt lost, or perhaps were lost. What did that feel like? Often a good simile is one that makes an unexpected comparison. For me, I can remember getting lost when I was young at a baseball game, and the feeling of panic I felt being among so many people, none of whom I knew or who cared anything about me. For the first time, I was completely free of adult supervision, but at the same time this freedom was a kind of prison. I desperately wanted to find my parents. Is there a simile in this? Perhaps being lost is as if the whole world is your prison.
Do you have to come up with a few similes based on being lost? Well, a good place to start is to remember that similes compare one thing or action with something else that we normally wouldn't associate with the first object or action that is being described. This helps us to look at the first object or action in a completely different way. So, you might like to think about the state of being lost. Do you have any memories of being lost that you can draw upon? What did it feel like?
For me, I remember being lost in a supermarket when I was small and not able to find my mother. Because I was so young, I remember these shelves towering above me as if they were walls, and it felt like a labyrinth or some kind of maze. Therefore I would describe the experience of being lost like being trapped in a maze from which there is no escape. Of course, depending on the context, you might come up with a different simile. Hope this helps, and good luck!