Should I start to do social media by myself or get help from agency?

you try and you learn :)

It depends upon your goals, budget, and how complicated your problem is.

The purpose of social media is also to get people to know more about your company/ products/ services. And for that reason, it's another way of "advertising". However, it is not exactly the same and that's why it has a different name.

Using a service agency or your staff it depends on your view and strategy. For instant (for self running), do you have enough resource for self running this? or in other words, if you run this, does it impact to your daily operation? another note worthy factor is that this also as a double blade knife as it has high potential for media crisis due to your limited ability/ expertise in this kind of work. Typical example that you can observe from other forums that some customers complaint about a company's service/ product, then immediately their staff jump in and have extreme defense actions. For using agency, to cope with same content issue as mentioned earlier why don't you try to discuss with the agency that you want to deliver a certain set of messages about your products rather than a set of approved fixed messages to be printed or posted on the network? This means the same core message but it can be exployed from different angles.

Further clarification requires, kindly let me know. Good luck!
Cheers,

they are right, depends what you want to do?
Should you do trapeze with a safety net? Most people will tell you YES. But it is NO if your purpose is to quit this life.
If you can afford to fail go trying, read and get a coach to learn while you do. As you call it a campaign!
But social media is not for selling, it is made to create awareness and channel interest towards your product. It cannot be a campaign, or if it is aim at 2-3 years to see significant sales.
Now if you are building a brand you cannot afford to fail due to trials and errors, because you will be haunted by your mistakes. Your company or products will get parasite bites from.

Reading and coaching definitely will save you times and big mistakes of the beginners...

The social media is a modern tool of marketer nowaday. It require the manager must be understand & have times to its control cause the connections that it maken. Agency give you the times & create more way to adtract your target customer but you have to give them your aims & lead the contents what you want to publish on that social media. This tool have good & bad effect, so the relationship between your company & agency