Hi! It is completely normal to feel unsafe or nervous about travelling alone, especially if you have no experience yet. I am not a woman so I can't give you advice that applies specifically to your situation (I am sure there are many solo female travellers on this sub who can help you out with that though) but I can tell you a few things that helped me when I first went abroad Han style.

- Understand that you will not be alone, even if you are leaving without any travel partners. Unless you are planning to a very remote or unusual location there will be many more travellers. There will be people working in the tourism business. There will be locals. Especially if you're staying in hostels you will make friends quickly and the feeling of being alone will fade quickly.

- Crimes like the one you describe are not as prevalent as you think. There are thousands and thousands of solo female travellers who do not get raped/abucted/murdered. You only hear about the stories that went wrong because "Lady travels alone by herself, has a great time" doesn't make for a good headline.

- (Clicé incoming) The vast majority of people in any location you're travelling to will be normal people living normal lives doing normal stuff. Crime might be more rampant in some destinations, especially in developing countries, but it's not like you're going to be travelling to a 18th century pirate republic where everybody is a criminal.

- Most crime in developing countries happens in places that you have absolutely no reason to ever go. Stay away from the poorest neighbourhoods, stick to the touristy center and you will most likely not encounter any crime in the first place.

I hope I managed to reassure you even a small bit! If you share with us where you plan on travelling to maybe we can give you more specific advice. You might also consider xposting to /r/solotravel for more exposure.