I have 1 customer

for Social Media Services. How to get more jobs? 

You have 1 client, wonderful. Repeat that process and you’ll get more!
From my experience, finding clients is a different process than applying for a job.
Job = resume 
For a job, you want to make sure the words in your resume fit with the job vacancy.
Clients = solving problems 
To find clients, you want to focus on what problems you are solving for them. And being unique in what you offer. 
How do you provide value as 
* social media manager
* virtual assistant
What makes you different?
What are the key issues companies have within this role?
Do a Quick google search for the specific job you are after: 
When do people hire a social media manager?
Issues with hiring online?
Etc… understand the issues your customers have and make sure you solve the problem. Talk about them. Look for them online. 
Could this be YOUR Dream job?