1. Missing someone:
* Je te manque. (Formal/Informal) - This literally means "I miss you."
* Tu me manques. (Formal/Informal) - This literally means "You miss me."
2. Missing something:
* Il me manque quelque chose. (Formal) - This means "I am missing something."
* Il me manque... (Informal) - This means "I am missing..." followed by the thing you are missing. For example, "Il me manque mon livre" means "I am missing my book."
3. Being lost or absent:
* Je suis perdu(e). (Formal/Informal) - This means "I am lost."
* Je suis absent(e). (Formal/Informal) - This means "I am absent."
4. Being lost, missing, or absent figuratively:
* Je me sens perdu(e). (Formal/Informal) - This means "I feel lost."
* Il me manque quelque chose dans ma vie. (Formal/Informal) - This means "I am missing something in my life."
The best translation will depend on what you are trying to convey.