A Teen Sim can run away from the household when the particular teen has negative Relationships with the other members of the household, and has few or no other friends. When a teen is preparing to leave, a message will pop up in the upper-right hand corner letting the player know. Then, the teen either walks or runs off of the lot. The memory associated with a teen running away is usually red but may also be green depending on the Sim and their relationship with the teen. While running away, a runaway icon will appear on their picture. Being gone does not affect things like school grades.
If a player wants the teen to return as soon as possible, the parents of the teen must report the runaway via telephone to the police. Doing this will increase chances of the runaway being returned by the police. If the teen is reported after twenty-four hours, the chances of being returned by the police decrease to about fifty-percent. If the teen is returned by the police, he/she will not run away again for more than twenty-four hours. If nothing is done about the run away, the teen will return home one day before they Grow up, and will not run away again.
- Having a low relationship with all other Sims/Pets on the lot.
- Witnessing a fire.
- Losing a fight with another pet.
- Their motives are too low.
- A Sim who they see as their Master dies.
Getting a runaway pet back follows the same steps as with teens. A unique memory will be added to the memories of other Sims upon running away, and another when the pet returns. If the pet has a collar, there is a chance that the pet will be found and returned even if it was not reported as having run away.
In The Sims 3: Pets, pets will run away if a fire breaks loose, if their relationships with the household Sims are low, or if their mood is too low. Lost pets leave a bad moodlet that lasts until the pet is found. Sims may find their pets wandering around town, and their moodlets can indicate where they are. For example, when a pet is at the library, the moodlet associated with libraries will be present.