Yes, absolutely! Under no circumstances should you sign a lease without your roommates! All tenants need to sign the lease and understand the contract each tenant is liable for. If choosing to sign a lease without having roommates ready, the tenant would be liable for the entirety of the rent if unable to find roommates, or if roommates not on the lease fail to pay their rent or follow the terms of the lease.
More information on roommates, including tips for finding roommates, can be found in Step 3: Roommates of our Rental Timeline.